Leverage MinGW's llrint() in Cygwin compilations.

Originally committed as revision 10878 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/general.texi

@@ -530,27 +530,36 @@ Then you can easily test FFmpeg with Wine
 
 @subsection Compilation under Cygwin
 
-Cygwin works very much like Unix.
+The main issue with Cygwin is that newlib, its C library, does not
+contain llrint().  However, it is possible to leverage the
+implementation in MinGW.
 
 Just install your Cygwin with all the "Base" packages, plus the
 following "Devel" ones:
 @example
-binutils, gcc-core, make, subversion
+binutils, gcc-core, make, subversion, mingw-runtime
 @end example
 
 Do not install binutils-20060709-1 (they are buggy on shared builds);
 use binutils-20050610-1 instead.
 
+Then create a small library that just contains llrint():
+
+@example
+ar x /usr/lib/mingw/libmingwex.a llrint.o
+ar cq /usr/local/lib/libllrint.a llrint.o
+@end example
+
 Then run
 
 @example
-./configure --enable-static --disable-shared
+./configure --enable-static --disable-shared  --extra-ldflags='-L /usr/local/lib' --extra-libs='-l llrint'
 @end example
 
 to make a static build or
 
 @example
-./configure --enable-shared --disable-static
+./configure --enable-shared --disable-static  --extra-ldflags='-L /usr/local/lib' --extra-libs='-l llrint'
 @end example
 
 to build shared libraries.