configure

        _type=armasm
        _ident=$($_cc | head -n1)
        # 4509: "This form of conditional instruction is deprecated"
        _flags="-nologo -ignore 4509"
        _flags_filter=armasm_flags
    elif $_cc 2>&1 | grep -q Intel; then
        _type=icl
        _ident=$($_cc 2>&1 | head -n1)
        _depflags='-QMMD -QMF$(@:.o=.d) -QMT$@'
        # Not only is O3 broken on 13.x+ but it is slower on all previous
        # versions (tested) as well.
        _cflags_speed="-O2"
        _cflags_size="-O1 -Oi" # -O1 without -Oi miscompiles stuff
        if $_cc 2>&1 | grep -q Linker; then
            _ld_o='-out:$@'
        else
            _ld_o='-Fe$@'
        fi
        _cc_o='-Fo$@'
        _cc_e='-P'
        _flags_filter=icl_flags
        _ld_lib='lib%.a'
        _ld_path='-libpath:'
        # -Qdiag-error to make icl error when seeing certain unknown arguments
        _flags='-nologo -Qdiag-error:4044,10157'
        # -Qvec- -Qsimd- to prevent miscompilation, -GS, fp:precise for consistency
        # with MSVC which enables it by default.
        _cflags='-D_USE_MATH_DEFINES -Qms0 -Qvec- -Qsimd- -GS -fp:precise'
        disable stripping
    elif $_cc -nologo- 2>&1 | grep -q Microsoft; then
        _type=msvc
        _ident=$($_cc 2>&1 | head -n1)
        _DEPCMD='$(DEP$(1)) $(DEP$(1)FLAGS) $($(1)DEP_FLAGS) $< 2>&1 | awk '\''/including/ { sub(/^.*file: */, ""); gsub(/\\/, "/"); if (!match($$0, / /)) print "$@:", $$0 }'\'' > $(@:.o=.d)'
        _DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
        _cflags_speed="-O2"
        _cflags_size="-O1"
        if $_cc -nologo- 2>&1 | grep -q Linker; then
            _ld_o='-out:$@'
        else
            _ld_o='-Fe$@'
        fi
        _cc_o='-Fo$@'
        _cc_e='-P -Fi$@'
        _flags_filter=msvc_flags
        _ld_lib='lib%.a'
        _ld_path='-libpath:'
        _flags='-nologo'
        _cflags='-D_USE_MATH_DEFINES -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS'
        disable stripping
    elif $_cc --version 2>/dev/null | grep -q ^cparser; then
        _type=cparser
        _ident=$($_cc --version | head -n1)
        _depflags='-MMD'
        _cflags_speed='-O4'
        _cflags_size='-O2'
        _flags_filter=cparser_flags
    fi

    eval ${pfx}_type=\$_type
    eval ${pfx}_ident=\$_ident
}

set_ccvars(){
    eval ${1}_C=\${_cc_c-\${${1}_C}}
    eval ${1}_E=\${_cc_e-\${${1}_E}}
    eval ${1}_O=\${_cc_o-\${${1}_O}}

    if [ -n "$_depflags" ]; then
        eval ${1}_DEPFLAGS=\$_depflags
    else
        eval ${1}DEP=\${_DEPCMD:-\$DEPCMD}
        eval ${1}DEP_FLAGS=\${_DEPFLAGS:-\$DEPFLAGS}
        eval DEP${1}FLAGS=\$_flags
    fi
}

probe_cc cc "$cc" "true"
cflags_filter=$_flags_filter
cflags_speed=$_cflags_speed
cflags_size=$_cflags_size
cflags_noopt=$_cflags_noopt
add_cflags $_flags $_cflags
cc_ldflags=$_ldflags
set_ccvars CC

probe_cc hostcc "$host_cc"
host_cflags_filter=$_flags_filter
add_host_cflags  $_flags $_cflags
set_ccvars HOSTCC

test -n "$cc_type" && enable $cc_type ||
    warn "Unknown C compiler $cc, unable to select optimal CFLAGS"

: ${as_default:=$cc}
: ${objcc_default:=$cc}
: ${dep_cc_default:=$cc}
: ${ld_default:=$cc}
: ${host_ld_default:=$host_cc}
set_default ar as objcc dep_cc ld ln_s host_ld windres

probe_cc as "$as"
asflags_filter=$_flags_filter
add_asflags $_flags $_cflags
set_ccvars AS

probe_cc objcc "$objcc"
objcflags_filter=$_flags_filter
add_objcflags $_flags $_cflags
set_ccvars OBJC

probe_cc ld "$ld"
ldflags_filter=$_flags_filter
add_ldflags $_flags $_ldflags
test "$cc_type" != "$ld_type" && add_ldflags $cc_ldflags
LD_O=${_ld_o-$LD_O}
LD_LIB=${_ld_lib-$LD_LIB}
LD_PATH=${_ld_path-$LD_PATH}

probe_cc hostld "$host_ld"
host_ldflags_filter=$_flags_filter
add_host_ldflags $_flags $_ldflags
HOSTLD_O=${_ld_o-$HOSTLD_O}

if [ -z "$CC_DEPFLAGS" ] && [ "$dep_cc" != "$cc" ]; then
    probe_cc depcc "$dep_cc"
    CCDEP=${_DEPCMD:-$DEPCMD}
    CCDEP_FLAGS=${_DEPFLAGS:=$DEPFLAGS}
    DEPCCFLAGS=$_flags
fi

if $ar 2>&1 | grep -q Microsoft; then
    arflags="-nologo"
    ar_o='-out:$@'
elif $ar 2>&1 | grep -q 'Texas Instruments'; then
    arflags="rq"
    ar_o='$@'
elif $ar 2>&1 | grep -q 'Usage: ar.*-X.*any'; then
    arflags='-Xany -r -c'
    ar_o='$@'
elif $ar 2>&1 | grep -q "\[D\] "; then
    arflags="rcD"
    ar_o='$@'
else
    arflags="rc"
    ar_o='$@'
fi

add_cflags $extra_cflags
add_cxxflags $extra_cxxflags
add_objcflags $extra_objcflags
add_asflags $extra_cflags

if test -n "$sysroot"; then
    case "$cc_type" in
        gcc|llvm_gcc|clang)
            add_cppflags --sysroot="$sysroot"
            add_ldflags --sysroot="$sysroot"
# On Darwin --sysroot may be ignored, -isysroot always affects headers and linking
            add_cppflags -isysroot "$sysroot"
            add_ldflags -isysroot "$sysroot"
        ;;
        tms470)
            add_cppflags -I"$sysinclude"
            add_ldflags  --sysroot="$sysroot"
        ;;
    esac
fi

if test "$cpu" = host; then
    enabled cross_compile &&
        die "--cpu=host makes no sense when cross-compiling."

    case "$cc_type" in
        gcc|llvm_gcc)
            check_native(){
                $cc $1=native -v -c -o $TMPO $TMPC >$TMPE 2>&1 || return
                sed -n "/cc1.*$1=/{
                            s/.*$1=\\([^ ]*\\).*/\\1/
                            p
                            q
                        }" $TMPE
            }
            cpu=$(check_native -march || check_native -mcpu)
        ;;
        clang)
            check_native(){
                $cc $1=native -v -c -o $TMPO $TMPC >$TMPE 2>&1 || return
                sed -n "/cc1.*-target-cpu /{
                            s/.*-target-cpu \\([^ ]*\\).*/\\1/
                            p
                            q
                        }" $TMPE
            }
            cpu=$(check_native -march)
        ;;
    esac

    test "${cpu:-host}" = host &&
        die "--cpu=host not supported with compiler $cc"
fi

# Deal with common $arch aliases
case "$arch" in
    aarch64|arm64)
        arch="aarch64"
    ;;
    arm*|iPad*|iPhone*)
        arch="arm"
    ;;
    mips*|IP*)
        case "$arch" in
        *el)
            add_cppflags -EL
            add_ldflags -EL
        ;;
        *eb)
            add_cppflags -EB
            add_ldflags -EB
        ;;
        esac
        arch="mips"
    ;;
    parisc*|hppa*)
        arch="parisc"
    ;;
    "Power Macintosh"|ppc*|powerpc*)
        arch="ppc"
    ;;
    s390|s390x)
        arch="s390"
    ;;
    sh4|sh)
        arch="sh4"
    ;;
    sun4*|sparc*)
        arch="sparc"
    ;;
    tilegx|tile-gx)
        arch="tilegx"
    ;;
    i[3-6]86*|i86pc|BePC|x86pc|x86_64|x86_32|amd64)
        arch="x86"
    ;;
esac

is_in $arch $ARCH_LIST || warn "unknown architecture $arch"
enable $arch

# Add processor-specific flags
if enabled aarch64; then

    case $cpu in
        armv*)
            cpuflags="-march=$cpu"
        ;;
        *)
            cpuflags="-mcpu=$cpu"
        ;;
    esac

elif enabled alpha; then

    cpuflags="-mcpu=$cpu"

elif enabled arm; then

    check_arm_arch() {
        check_cpp_condition stddef.h \
            "defined __ARM_ARCH_${1}__ || defined __TARGET_ARCH_${2:-$1}" \
            $cpuflags
    }

    probe_arm_arch() {
        if   check_arm_arch 4;        then echo armv4
        elif check_arm_arch 4T;       then echo armv4t
        elif check_arm_arch 5;        then echo armv5
        elif check_arm_arch 5E;       then echo armv5e
        elif check_arm_arch 5T;       then echo armv5t
        elif check_arm_arch 5TE;      then echo armv5te
        elif check_arm_arch 5TEJ;     then echo armv5te
        elif check_arm_arch 6;        then echo armv6
        elif check_arm_arch 6J;       then echo armv6j
        elif check_arm_arch 6K;       then echo armv6k
        elif check_arm_arch 6Z;       then echo armv6z
        elif check_arm_arch 6ZK;      then echo armv6zk
        elif check_arm_arch 6T2;      then echo armv6t2
        elif check_arm_arch 7;        then echo armv7
        elif check_arm_arch 7A  7_A;  then echo armv7-a
        elif check_arm_arch 7S;       then echo armv7-a
        elif check_arm_arch 7R  7_R;  then echo armv7-r
        elif check_arm_arch 7M  7_M;  then echo armv7-m
        elif check_arm_arch 7EM 7E_M; then echo armv7-m
        elif check_arm_arch 8A  8_A;  then echo armv8-a
        fi
    }

    [ "$cpu" = generic ] && cpu=$(probe_arm_arch)

    case $cpu in
        armv*)
            cpuflags="-march=$cpu"
            subarch=$(echo $cpu | sed 's/[^a-z0-9]//g')
        ;;
        *)
            cpuflags="-mcpu=$cpu"
            case $cpu in
                cortex-a*)                               subarch=armv7a  ;;
                cortex-r*)                               subarch=armv7r  ;;
                cortex-m*)                 enable thumb; subarch=armv7m  ;;
                arm11*)                                  subarch=armv6   ;;
                arm[79]*e*|arm9[24]6*|arm96*|arm102[26]) subarch=armv5te ;;
                armv4*|arm7*|arm9[24]*)                  subarch=armv4   ;;
                *)                             subarch=$(probe_arm_arch) ;;
            esac
        ;;
    esac

    case "$subarch" in
        armv5t*)    enable fast_clz                ;;
        armv[6-8]*)
            enable fast_clz
            disabled fast_unaligned || enable fast_unaligned
            ;;
    esac

elif enabled avr32; then

    case $cpu in
        ap7[02]0[0-2])
            subarch="avr32_ap"
            cpuflags="-mpart=$cpu"
        ;;
        ap)
            subarch="avr32_ap"
            cpuflags="-march=$cpu"
        ;;
        uc3[ab]*)
            subarch="avr32_uc"
            cpuflags="-mcpu=$cpu"
        ;;
        uc)
            subarch="avr32_uc"
            cpuflags="-march=$cpu"
        ;;
    esac

elif enabled bfin; then

    cpuflags="-mcpu=$cpu"

elif enabled mips; then

    cpuflags="-march=$cpu"

    if [ "$cpu" != "generic" ]; then
        disable mips32r2
        disable mips32r5
        disable mips64r2
        disable mips32r6
        disable mips64r6
        disable loongson2
        disable loongson3

        case $cpu in
            24kc|24kf*|24kec|34kc|1004kc|24kef*|34kf*|1004kf*|74kc|74kf)
                enable mips32r2
                disable msa
            ;;
            p5600|i6400|p6600)
                disable mipsdsp
                disable mipsdspr2
            ;;
            loongson*)
                enable loongson2
                enable loongson3
                enable local_aligned_8 local_aligned_16 local_aligned_32
                enable simd_align_16
                enable fast_64bit
                enable fast_clz
                enable fast_cmov
                enable fast_unaligned
                disable aligned_stack
                disable mipsfpu
                disable mipsdsp
                disable mipsdspr2
                case $cpu in
                    loongson3*)
                        cpuflags="-march=loongson3a -mhard-float -fno-expensive-optimizations"
                    ;;
                    loongson2e)
                        cpuflags="-march=loongson2e -mhard-float -fno-expensive-optimizations"
                    ;;
                    loongson2f)
                        cpuflags="-march=loongson2f -mhard-float -fno-expensive-optimizations"
                    ;;
                esac
            ;;
            *)
                # Unknown CPU. Disable everything.
                warn "unknown CPU. Disabling all MIPS optimizations."
                disable mipsfpu
                disable mipsdsp
                disable mipsdspr2
                disable msa
                disable mmi
            ;;
        esac

        case $cpu in
            24kc)
                disable mipsfpu
                disable mipsdsp
                disable mipsdspr2
            ;;
            24kf*)
                disable mipsdsp
                disable mipsdspr2
            ;;
            24kec|34kc|1004kc)
                disable mipsfpu
                disable mipsdspr2
            ;;
            24kef*|34kf*|1004kf*)
                disable mipsdspr2
            ;;
            74kc)
                disable mipsfpu
            ;;
            p5600)
                enable mips32r5
                check_cflags "-mtune=p5600" && check_cflags "-msched-weight -mload-store-pairs -funroll-loops"
            ;;
            i6400)
                enable mips64r6
                check_cflags "-mtune=i6400 -mabi=64" && check_cflags "-msched-weight -mload-store-pairs -funroll-loops" && check_ldflags "-mabi=64"
            ;;
            p6600)
                enable mips64r6
                check_cflags "-mtune=p6600 -mabi=64" && check_cflags "-msched-weight -mload-store-pairs -funroll-loops" && check_ldflags "-mabi=64"
            ;;
        esac
    else
        # We do not disable anything. Is up to the user to disable the unwanted features.
        warn 'generic cpu selected'
    fi

elif enabled ppc; then

    disable ldbrx

    case $(tolower $cpu) in
        601|ppc601|powerpc601)
            cpuflags="-mcpu=601"
            disable altivec
        ;;
        603*|ppc603*|powerpc603*)
            cpuflags="-mcpu=603"
            disable altivec
        ;;
        604*|ppc604*|powerpc604*)
            cpuflags="-mcpu=604"
            disable altivec
        ;;
        g3|75*|ppc75*|powerpc75*)
            cpuflags="-mcpu=750"
            disable altivec
        ;;
        g4|745*|ppc745*|powerpc745*)
            cpuflags="-mcpu=7450"
            disable vsx
        ;;
        74*|ppc74*|powerpc74*)
            cpuflags="-mcpu=7400"
            disable vsx
        ;;
        g5|970|ppc970|powerpc970)
            cpuflags="-mcpu=970"
            disable vsx
        ;;
        power[3-6]*)
            cpuflags="-mcpu=$cpu"
            disable vsx
        ;;
        power[7-8]*)
            cpuflags="-mcpu=$cpu"
        ;;
        cell)
            cpuflags="-mcpu=cell"
            enable ldbrx
            disable vsx
        ;;
        e500mc)
            cpuflags="-mcpu=e500mc"
            disable altivec
        ;;
        e500v2)
            cpuflags="-mcpu=8548 -mhard-float -mfloat-gprs=double"
            disable altivec
            disable dcbzl
        ;;
        e500)
            cpuflags="-mcpu=8540 -mhard-float"
            disable altivec
            disable dcbzl
        ;;
    esac

elif enabled sparc; then

    case $cpu in
        cypress|f93[04]|tsc701|sparcl*|supersparc|hypersparc|niagara|v[789])
            cpuflags="-mcpu=$cpu"
        ;;
        ultrasparc*|niagara[234])
            cpuflags="-mcpu=$cpu"
        ;;
    esac

elif enabled x86; then

    case $cpu in
        i[345]86|pentium)
            cpuflags="-march=$cpu"
            disable i686
            disable mmx
        ;;
        # targets that do NOT support nopl and conditional mov (cmov)
        pentium-mmx|k6|k6-[23]|winchip-c6|winchip2|c3)
            cpuflags="-march=$cpu"
            disable i686
        ;;
        # targets that do support nopl and conditional mov (cmov)
        i686|pentiumpro|pentium[23]|pentium-m|athlon|athlon-tbird|athlon-4|athlon-[mx]p|athlon64*|k8*|opteron*|athlon-fx\
        |core*|atom|bonnell|nehalem|westmere|silvermont|sandybridge|ivybridge|haswell|broadwell|skylake*|knl\
        |amdfam10|barcelona|b[dt]ver*|znver*)
            cpuflags="-march=$cpu"
            enable i686
            enable fast_cmov
        ;;
        # targets that do support conditional mov but on which it's slow
        pentium4|pentium4m|prescott|nocona)
            cpuflags="-march=$cpu"
            enable i686
            disable fast_cmov
        ;;
    esac

fi

if [ "$cpu" != generic ]; then
    add_cflags  $cpuflags
    add_asflags $cpuflags
    test "$cc_type" = "$ld_type" && add_ldflags $cpuflags
fi

# compiler sanity check
check_exec <<EOF
int main(void){ return 0; }
EOF
if test "$?" != 0; then
    echo "$cc is unable to create an executable file."
    if test -z "$cross_prefix" && ! enabled cross_compile ; then
        echo "If $cc is a cross-compiler, use the --enable-cross-compile option."
        echo "Only do this if you know what cross compiling means."
    fi
    die "C compiler test failed."
fi

add_cppflags -D_ISOC99_SOURCE
add_cxxflags -D__STDC_CONSTANT_MACROS
add_cxxflags -std=c++98
check_cflags -std=c99
check_cc -D_FILE_OFFSET_BITS=64 <<EOF && add_cppflags -D_FILE_OFFSET_BITS=64
#include <stdlib.h>
EOF
check_cc -D_LARGEFILE_SOURCE <<EOF && add_cppflags -D_LARGEFILE_SOURCE
#include <stdlib.h>
EOF

add_host_cppflags -D_ISOC99_SOURCE
check_host_cflags -std=c99
check_host_cflags -Wall
check_host_cflags -O3

check_64bit(){
    arch32=$1
    arch64=$2
    expr=$3
    check_code cc "" "int test[2*($expr) - 1]" &&
        subarch=$arch64 || subarch=$arch32
}

case "$arch" in
    aarch64|alpha|ia64)
        spic=$shared
    ;;
    mips)
        check_64bit mips mips64 '_MIPS_SIM > 1'
        spic=$shared
    ;;
    parisc)
        check_64bit parisc parisc64 'sizeof(void *) > 4'
        spic=$shared
    ;;
    ppc)
        check_64bit ppc ppc64 'sizeof(void *) > 4'
        spic=$shared
    ;;
    s390)
        check_64bit s390 s390x 'sizeof(void *) > 4'
        spic=$shared
    ;;
    sparc)
        check_64bit sparc sparc64 'sizeof(void *) > 4'
        spic=$shared
    ;;
    x86)
        check_64bit x86_32 x86_64 'sizeof(void *) > 4'
        # Treat x32 as x64 for now. Note it also needs spic=$shared
        test "$subarch" = "x86_32" && check_cpp_condition stddef.h 'defined(__x86_64__)' &&
            subarch=x86_64
        if test "$subarch" = "x86_64"; then
            spic=$shared
        fi
    ;;
    ppc)
        check_cc <<EOF && subarch="ppc64"
        int test[(int)sizeof(char*) - 7];
EOF
    ;;
esac

enable $subarch
enabled spic && enable_weak pic

# OS specific
case $target_os in
    aix)
        SHFLAGS=-shared
        add_cppflags '-I\$(SRC_PATH)/compat/aix'
        enabled shared && add_ldflags -Wl,-brtl
        ;;
    android)
        disable symver
        enable section_data_rel_ro
        SLIB_INSTALL_NAME='$(SLIBNAME)'
        SLIB_INSTALL_LINKS=
        SHFLAGS='-shared -Wl,-soname,$(SLIBNAME)'
        ;;
    haiku)
        prefix_default="/boot/common"
        network_extralibs="-lnetwork"
        host_libs=
        ;;
    sunos)
        SHFLAGS='-shared -Wl,-h,$$(@F)'
        enabled x86 && SHFLAGS="-mimpure-text $SHFLAGS"
        network_extralibs="-lsocket -lnsl"
        add_cppflags -D__EXTENSIONS__
        # When using suncc to build, the Solaris linker will mark
        # an executable with each instruction set encountered by
        # the Solaris assembler.  As our libraries contain their own
        # guards for processor-specific code, instead suppress
        # generation of the HWCAPS ELF section on Solaris x86 only.
        enabled_all suncc x86 &&
            echo "hwcap_1 = OVERRIDE;" > mapfile &&
            add_ldflags -Wl,-M,mapfile
        nm_default='nm -P -g'
        version_script='-M'
        VERSION_SCRIPT_POSTPROCESS_CMD='perl $(SRC_PATH)/compat/solaris/make_sunver.pl - $(OBJS)'
        ;;
    netbsd)
        disable symver
        oss_indev_extralibs="-lossaudio"
        oss_outdev_extralibs="-lossaudio"
        enabled gcc || check_ldflags -Wl,-zmuldefs
        ;;
    openbsd|bitrig)
        disable symver
        SHFLAGS='-shared'
        SLIB_INSTALL_NAME='$(SLIBNAME).$(LIBMAJOR).$(LIBMINOR)'
        SLIB_INSTALL_LINKS=
        oss_indev_extralibs="-lossaudio"
        oss_outdev_extralibs="-lossaudio"
        ;;
    dragonfly)
        disable symver
        ;;
    freebsd)
        ;;
    bsd/os)
        add_extralibs -lpoll -lgnugetopt
        strip="strip -d"
        ;;
    darwin)
        enabled ppc && add_asflags -force_cpusubtype_ALL
        install_name_dir_default='$(SHLIBDIR)'
        SHFLAGS='-dynamiclib -Wl,-single_module -Wl,-install_name,$(INSTALL_NAME_DIR)/$(SLIBNAME_WITH_MAJOR),-current_version,$(LIBVERSION),-compatibility_version,$(LIBMAJOR)'
        enabled x86_32 && append SHFLAGS -Wl,-read_only_relocs,suppress
        strip="${strip} -x"
        add_ldflags -Wl,-dynamic,-search_paths_first
        SLIBSUF=".dylib"
        SLIBNAME_WITH_VERSION='$(SLIBPREF)$(FULLNAME).$(LIBVERSION)$(SLIBSUF)'
        SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME).$(LIBMAJOR)$(SLIBSUF)'
        objformat="macho"
        enabled x86_64 && objformat="macho64"
        enabled_any pic shared x86_64 ||
            { check_cflags -mdynamic-no-pic && add_asflags -mdynamic-no-pic; }
        check_header dispatch/dispatch.h &&
            add_cppflags '-I\$(SRC_PATH)/compat/dispatch_semaphore'
        version_script='-exported_symbols_list'
        VERSION_SCRIPT_POSTPROCESS_CMD='tr " " "\n" | sed -n /global:/,/local:/p | grep ";" | tr ";" "\n" | sed -E "s/(.+)/_\1/g" | sed -E "s/(.+[^*])$$$$/\1*/"'
        ;;
    msys*)
        die "Native MSYS builds are discouraged, please use the MINGW environment."
        ;;
    mingw32*|mingw64*)
        if test $target_os = "mingw32ce"; then
            disable network
        else
            target_os=mingw32
        fi
        decklink_outdev_extralibs="$decklink_outdev_extralibs -lole32 -loleaut32"
        decklink_indev_extralibs="$decklink_indev_extralibs -lole32 -loleaut32"
        LIBTARGET=i386
        if enabled x86_64; then
            LIBTARGET="i386:x86-64"
        elif enabled arm; then
            LIBTARGET=arm-wince
        fi
        enabled shared && ! enabled small && check_cmd $windres --version && enable gnu_windres
        enabled x86_32 && check_ldflags -Wl,--large-address-aware
        shlibdir_default="$bindir_default"
        SLIBPREF=""
        SLIBSUF=".dll"
        SLIBNAME_WITH_VERSION='$(SLIBPREF)$(FULLNAME)-$(LIBVERSION)$(SLIBSUF)'
        SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
        dlltool="${cross_prefix}dlltool"
        if check_cmd lib.exe -list; then
            SLIB_EXTRA_CMD=-'sed -e "s/ @[^ ]*//" $$(@:$(SLIBSUF)=.orig.def) > $$(@:$(SLIBSUF)=.def); lib.exe /machine:$(LIBTARGET) /def:$$(@:$(SLIBSUF)=.def) /out:$(SUBDIR)$(SLIBNAME:$(SLIBSUF)=.lib)'
            if enabled x86_64; then
                LIBTARGET=x64
            fi
        elif check_cmd $dlltool --version; then
            SLIB_EXTRA_CMD=-'sed -e "s/ @[^ ]*//" $$(@:$(SLIBSUF)=.orig.def) > $$(@:$(SLIBSUF)=.def); $(DLLTOOL) -m $(LIBTARGET) -d $$(@:$(SLIBSUF)=.def) -l $(SUBDIR)$(SLIBNAME:$(SLIBSUF)=.lib) -D $(SLIBNAME_WITH_MAJOR)'
        fi
        SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
        SLIB_INSTALL_LINKS=
        SLIB_INSTALL_EXTRA_SHLIB='$(SLIBNAME:$(SLIBSUF)=.lib)'
        SLIB_INSTALL_EXTRA_LIB='lib$(SLIBNAME:$(SLIBSUF)=.dll.a) $(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.def)'
        SHFLAGS='-shared -Wl,--output-def,$$(@:$(SLIBSUF)=.orig.def) -Wl,--out-implib,$(SUBDIR)lib$(SLIBNAME:$(SLIBSUF)=.dll.a) -Wl,--enable-runtime-pseudo-reloc -Wl,--disable-auto-image-base'
        objformat="win32"
        ranlib=:
        enable dos_paths
        check_ldflags -Wl,--nxcompat,--dynamicbase
        # Lets work around some stupidity in binutils.
        # ld will strip relocations from executables even though we need them
        # for dynamicbase (ASLR).  Using -pie does retain the reloc section
        # however ld then forgets what the entry point should be (oops) so we
        # have to manually (re)set it.
        if enabled x86_32; then
            disabled debug && add_ldexeflags -Wl,--pic-executable,-e,_mainCRTStartup
        elif enabled x86_64; then
            disabled debug && add_ldexeflags -Wl,--pic-executable,-e,mainCRTStartup
            check_ldflags -Wl,--high-entropy-va # binutils 2.25
            # Set image base >4GB for extra entropy with HEASLR
            add_ldexeflags -Wl,--image-base,0x140000000
            append SHFLAGS -Wl,--image-base,0x180000000
        fi
        ;;
    win32|win64)
        disable symver
        if enabled shared; then
            # Link to the import library instead of the normal static library
            # for shared libs.
            LD_LIB='%.lib'
            # Cannot build both shared and static libs with MSVC or icl.
            disable static
        fi
        enabled x86_32 && check_ldflags -LARGEADDRESSAWARE
        shlibdir_default="$bindir_default"
        SLIBPREF=""
        SLIBSUF=".dll"
        SLIBNAME_WITH_VERSION='$(SLIBPREF)$(FULLNAME)-$(LIBVERSION)$(SLIBSUF)'
        SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
        SLIB_CREATE_DEF_CMD='$(SRC_PATH)/compat/windows/makedef $(SUBDIR)lib$(NAME).ver $(OBJS) > $$(@:$(SLIBSUF)=.def)'
        SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
        SLIB_INSTALL_LINKS=
        SLIB_INSTALL_EXTRA_SHLIB='$(SLIBNAME:$(SLIBSUF)=.lib)'
        SLIB_INSTALL_EXTRA_LIB='$(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.def)'
        SHFLAGS='-dll -def:$$(@:$(SLIBSUF)=.def) -implib:$(SUBDIR)$(SLIBNAME:$(SLIBSUF)=.lib)'
        objformat="win32"
        ranlib=:
        enable dos_paths
        ;;
    cygwin*)
        target_os=cygwin
        shlibdir_default="$bindir_default"
        SLIBPREF="cyg"
        SLIBSUF=".dll"
        SLIBNAME_WITH_VERSION='$(SLIBPREF)$(FULLNAME)-$(LIBVERSION)$(SLIBSUF)'
        SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
        SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
        SLIB_INSTALL_LINKS=
        SLIB_INSTALL_EXTRA_LIB='lib$(FULLNAME).dll.a'
        SHFLAGS='-shared -Wl,--out-implib,$(SUBDIR)lib$(FULLNAME).dll.a'
        objformat="win32"
        enable dos_paths
        enabled shared && ! enabled small && check_cmd $windres --version && enable gnu_windres
        add_cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
        ;;
    *-dos|freedos|opendos)
        network_extralibs="-lsocket"
        objformat="coff"
        enable dos_paths
        add_cppflags -U__STRICT_ANSI__
        ;;
    linux)
        enable dv1394
        enable section_data_rel_ro
        ;;
    irix*)
        target_os=irix
        ranlib="echo ignoring ranlib"
        ;;
    os/2*)
        strip="lxlite -CS"
        objformat="aout"
        add_cppflags -D_GNU_SOURCE
        add_ldflags -Zomf -Zbin-files -Zargs-wild -Zmap
        SHFLAGS='$(SUBDIR)$(NAME).def -Zdll -Zomf'
        LIBSUF="_s.a"
        SLIBPREF=""
        SLIBSUF=".dll"
        SLIBNAME_WITH_VERSION='$(SLIBPREF)$(FULLNAME)-$(LIBVERSION)$(SLIBSUF)'
        SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(shell echo $(FULLNAME) | cut -c1-6)$(LIBMAJOR)$(SLIBSUF)'
        SLIB_CREATE_DEF_CMD='echo LIBRARY $(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=) INITINSTANCE TERMINSTANCE > $(SUBDIR)$(FULLNAME).def; \
            echo CODE PRELOAD MOVEABLE DISCARDABLE >> $(SUBDIR)$(FULLNAME).def; \
            echo DATA PRELOAD MOVEABLE MULTIPLE NONSHARED >> $(SUBDIR)$(FULLNAME).def; \
            echo EXPORTS >> $(SUBDIR)$(FULLNAME).def; \
            emxexp $(OBJS) >> $(SUBDIR)$(FULLNAME).def'
        SLIB_EXTRA_CMD='emximp -o $(SUBDIR)$(LIBPREF)$(FULLNAME)_dll.a $(SUBDIR)$(FULLNAME).def; \
            emximp -o $(SUBDIR)$(LIBPREF)$(FULLNAME)_dll.lib $(SUBDIR)$(FULLNAME).def;'
        SLIB_INSTALL_NAME='$(SLIBNAME_WITH_MAJOR)'
        SLIB_INSTALL_LINKS=
        SLIB_INSTALL_EXTRA_LIB='$(LIBPREF)$(FULLNAME)_dll.a $(LIBPREF)$(FULLNAME)_dll.lib'
        enable dos_paths
        enable_weak os2threads
        ;;
    gnu/kfreebsd)
        add_cppflags -D_BSD_SOURCE
        ;;
    gnu)
        ;;
    qnx)
        add_cppflags -D_QNX_SOURCE
        network_extralibs="-lsocket"
        ;;
    symbian)
        SLIBSUF=".dll"
        enable dos_paths
        add_cflags --include=$sysinclude/gcce/gcce.h -fvisibility=default
        add_cppflags -D__GCCE__ -D__SYMBIAN32__ -DSYMBIAN_OE_POSIX_SIGNALS
        add_ldflags -Wl,--target1-abs,--no-undefined \
                    -Wl,-Ttext,0x80000,-Tdata,0x1000000 -shared \
                    -Wl,--entry=_E32Startup -Wl,-u,_E32Startup
        add_extralibs -l:eexe.lib -l:usrt2_2.lib -l:dfpaeabi.dso \
                      -l:drtaeabi.dso -l:scppnwdl.dso -lsupc++ -lgcc \
                      -l:libc.dso -l:libm.dso -l:euser.dso -l:libcrt0.lib
        ;;
    osf1)
        add_cppflags -D_OSF_SOURCE -D_POSIX_PII -D_REENTRANT
        ;;
    minix)
        ;;
    plan9)
        add_cppflags -D_C99_SNPRINTF_EXTENSION  \
                     -D_REENTRANT_SOURCE        \
                     -D_RESEARCH_SOURCE         \
                     -DFD_SETSIZE=96            \
                     -DHAVE_SOCK_OPTS
        add_compat strtod.o strtod=avpriv_strtod
        network_extralibs='-lbsd'
        exeobjs=compat/plan9/main.o
        disable ffserver
        cp_f='cp'
        ;;
    none)
        ;;
    *)
        die "Unknown OS '$target_os'."
        ;;
esac

# test if creating links works
link_dest=$(mktemp -u $TMPDIR/dest_XXXXXXXX)
link_name=$(mktemp -u $TMPDIR/name_XXXXXXXX)
mkdir "$link_dest"
$ln_s "$link_dest" "$link_name"
touch "$link_dest/test_file"
if [ "$source_path" != "." ] && ([ ! -d src ] || [ -L src ]) && [ -e "$link_name/test_file" ]; then
    # create link to source path
    [ -e src ] && rm src
    $ln_s "$source_path" src
    source_link=src
else
    # creating directory links doesn't work
    # fall back to using the full source path
    source_link="$source_path"
fi
# cleanup
rm -r "$link_dest"
rm -r "$link_name"

# determine libc flavour

probe_libc(){
    pfx=$1
    pfx_no_=${pfx%_}
    # uclibc defines __GLIBC__, so it needs to be checked before glibc.
    if check_${pfx}cpp_condition features.h "defined __UCLIBC__"; then
        eval ${pfx}libc_type=uclibc
        add_${pfx}cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
    elif check_${pfx}cpp_condition features.h "defined __GLIBC__"; then
        eval ${pfx}libc_type=glibc
        add_${pfx}cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
    # MinGW headers can be installed on Cygwin, so check for newlib first.
    elif check_${pfx}cpp_condition newlib.h "defined _NEWLIB_VERSION"; then
        eval ${pfx}libc_type=newlib
        add_${pfx}cppflags -U__STRICT_ANSI__
    # MinGW64 is backwards compatible with MinGW32, so check for it first.
    elif check_${pfx}cpp_condition _mingw.h "defined __MINGW64_VERSION_MAJOR"; then
        eval ${pfx}libc_type=mingw64
        if check_${pfx}cpp_condition _mingw.h "__MINGW64_VERSION_MAJOR < 3"; then
            add_compat msvcrt/snprintf.o
            add_cflags "-include $source_path/compat/msvcrt/snprintf.h"
        fi
        add_${pfx}cppflags -U__STRICT_ANSI__ -D__USE_MINGW_ANSI_STDIO=1
        eval test \$${pfx_no_}cc_type = "gcc" &&
            add_${pfx}cppflags -D__printf__=__gnu_printf__
    elif check_${pfx}cpp_condition _mingw.h "defined __MINGW_VERSION"  ||
         check_${pfx}cpp_condition _mingw.h "defined __MINGW32_VERSION"; then
        eval ${pfx}libc_type=mingw32
        check_${pfx}cpp_condition _mingw.h "__MINGW32_MAJOR_VERSION > 3 || \
            (__MINGW32_MAJOR_VERSION == 3 && __MINGW32_MINOR_VERSION >= 15)" ||
            die "ERROR: MinGW32 runtime version must be >= 3.15."
        add_${pfx}cppflags -U__STRICT_ANSI__ -D__USE_MINGW_ANSI_STDIO=1
        check_${pfx}cpp_condition _mingw.h "defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x0502" ||
            add_${pfx}cppflags -D_WIN32_WINNT=0x0502
        eval test \$${pfx_no_}cc_type = "gcc" &&
            add_${pfx}cppflags -D__printf__=__gnu_printf__
    elif check_${pfx}cpp_condition crtversion.h "defined _VC_CRT_MAJOR_VERSION"; then
        eval ${pfx}libc_type=msvcrt
        if check_${pfx}cpp_condition crtversion.h "_VC_CRT_MAJOR_VERSION < 14"; then
            if [ "$pfx" = host_ ]; then
                add_host_cppflags -Dsnprintf=_snprintf
            else
                add_compat strtod.o strtod=avpriv_strtod
                add_compat msvcrt/snprintf.o snprintf=avpriv_snprintf   \
                                             _snprintf=avpriv_snprintf  \
                                             vsnprintf=avpriv_vsnprintf
            fi
        fi
        # The MSVC 2010 headers (Win 7.0 SDK) set _WIN32_WINNT to
        # 0x601 by default unless something else is set by the user.
        # This can easily lead to us detecting functions only present
        # in such new versions and producing binaries requiring windows 7.0.
        # Therefore explicitly set the default to XP unless the user has
        # set something else on the command line.
        # Don't do this if WINAPI_FAMILY is set and is set to a non-desktop
        # family. For these cases, configure is free to use any functions
        # found in the SDK headers by default. (Alternatively, we could force
        # _WIN32_WINNT to 0x0602 in that case.)
        check_${pfx}cpp_condition stdlib.h "defined(_WIN32_WINNT)" ||
            { check_${pfx}cpp <<EOF && add_${pfx}cppflags -D_WIN32_WINNT=0x0502; }
#ifdef WINAPI_FAMILY
#include <winapifamily.h>
#if !WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
#error not desktop
#endif
#endif
EOF
    elif check_${pfx}cpp_condition stddef.h "defined __KLIBC__"; then
        eval ${pfx}libc_type=klibc
    elif check_${pfx}cpp_condition sys/cdefs.h "defined __BIONIC__"; then
        eval ${pfx}libc_type=bionic
    elif check_${pfx}cpp_condition sys/brand.h "defined LABELED_BRAND_NAME"; then
        eval ${pfx}libc_type=solaris
        add_${pfx}cppflags -D__EXTENSIONS__ -D_XOPEN_SOURCE=600
    fi
    check_${pfx}cc <<EOF
#include <time.h>
void *v = localtime_r;
EOF
test "$?" != 0 && check_${pfx}cc -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600 <<EOF && add_${pfx}cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
#include <time.h>
void *v = localtime_r;
EOF

}