Use -std=gnu11 instead of -std=gnu99.
Now that GCC 4.7 or later is required to build glibc, this patch moves
the build from using -std=gnu99 to -std=gnu11 (option added in 4.7).
This allows use of C11 features from GCC's headers, such as new
float.h macros and max_align_t.
Tested for x86_64 and x86 (testsuite; installed stripped shared
libraries are unchanged by the patch on x86_64, while I see some
slight code reordering of no significance on x86).
* Makeconfig (CFLAGS): Use -std=gnu11 instead of -std=gnu99.
* Makefile ($(objpfx)c++-types-check.out): Filter out -std=gnu11
instead of -std=gnu99.
* configure.ac (systemtap): Test with -std=gnu11 instead of
-std=gnu99.
* configure: Regenerated.
* math/gen-auto-libm-tests.c: Use -std=gnu11 instead of -std=gnu99
in compilation command in comment.