+
+if test "$cf_cv_gnu_source" = yes
+then
+AC_CACHE_CHECK(if we should also define _DEFAULT_SOURCE,cf_cv_default_source,[
+CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
+ AC_TRY_COMPILE([#include <sys/types.h>],[
+#ifdef _DEFAULT_SOURCE
+make an error
+#endif],
+ [cf_cv_default_source=no],
+ [cf_cv_default_source=yes])
+ ])
+test "$cf_cv_default_source" = yes && CPPFLAGS="$CPPFLAGS -D_DEFAULT_SOURCE"
+fi