[7 Regression] gnat bootstrap broken on linux targets with _FORTIFY_SOURCE enabled

[Matthias Klose]

seen with trunk r242874 on all linux architectures, and this patch to enable the build with -D_FORTIFY_SOURCE=2. This works on the gcc-6-branch, system glibc is 2.24.

--- a/gcc/c-family/c-cppbuiltin.c
+++ b/gcc/c-family/c-cppbuiltin.c
@@ -1176,6 +1176,10 @@ c_cpp_builtins (cpp_reader *pfile)
   builtin_define_with_value ("__REGISTER_PREFIX__", REGISTER_PREFIX, 0);
   builtin_define_with_value ("__USER_LABEL_PREFIX__", user_label_prefix, 0);

+ /* Fortify Source enabled by default for optimization levels > 0 */
+ if (optimize)
+ builtin_define_with_int_value ("_FORTIFY_SOURCE", 2);
+
   /* Misc. */
   if (flag_gnu89_inline)
     cpp_define (pfile, "__GNUC_GNU_INLINE__");