Re: use of __STDC_VERSION__ > foo in config.h

[Paul Eggert]

The general idea that config.h should work with -Wundef is OK
<http://lists.gnu.org/archive/html/bug-gnulib/2011-11/msg00308.html>
but I see a couple of problems with the proposed patch.
First, the logic is wrong, as it assumes that when 
__STDC_VERSION__ is not defined then the compiler supports C11,
whereas a better heuristic (these days, anyway) is that the compiler
does not support C11.  Second, there shouldn't be a need to alter
the code if it's an Apple compiler, since the problem has been
reported only for GCC.  So I pushed this smaller patch instead:

_Noreturn: port config.h to gcc -Wundef
* m4/gnulib-common.m4 (gl_COMMON_BODY): Check that __STDC_VERSION__ is
defined before using it, for gcc -Wundef.  Reported by Akim Demaille in
<http://lists.gnu.org/archive/html/bug-gnulib/2012-05/msg00147.html>.
diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4
index ab3c43d..d62b767 100644
--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -14,7 +14,8 @@ AC_DEFUN([gl_COMMON], [
 AC_DEFUN([gl_COMMON_BODY], [
   AH_VERBATIM([_Noreturn],
 [/* The _Noreturn keyword of C11.  */
-#if !defined _Noreturn && __STDC_VERSION__ < 201112
+#if ! (defined _Noreturn \
+       || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
 # if (3 <= __GNUC__ || (__GNUC__ == 2 && 8 <= __GNUC_MINOR__) \
       || 0x5110 <= __SUNPRO_C)
 #  define _Noreturn __attribute__ ((__noreturn__))