Add CFLAGS needed by PathScale compiler

The PathScale compiler miscompiles wrapping arithmetic without
these flags.

Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit 5f3b8314)

configure

@@ -2988,6 +2988,8 @@ elif enabled armcc; then
     add_cflags -W${armcc_opt},--diag_suppress=3343 # hardfp compat
 elif enabled tms470; then
     add_cflags -pds=824 -pds=837
+elif enabled pathscale; then
+    add_cflags -fstrict-overflow -OPT:wrap_around_unsafe_opt=OFF
 fi
 
 enabled_any $THREADS_LIST      && enable threads