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__))
