This is required to make certain math defines visible on modern Cygwin.
# 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__
+ add_${pfx}cppflags -U__STRICT_ANSI__ -D_XOPEN_SOURCE=600
# MinGW64 is backwards compatible with MinGW32, so check for it first.
elif check_${pfx}cpp_condition _mingw.h "defined __MINGW64_VERSION_MAJOR"; then
eval ${pfx}libc_type=mingw64