[PATCH] Fix Wundef warning for __STDC_VERSION__

[Roland McGrath]

> -#if !defined _Noreturn && __STDC_VERSION__ < 201112 && !__GNUC_PREREQ (4,7)
> +#if (!defined _Noreturn && defined __STDC_VERSION__ \
> +     && __STDC_VERSION__ < 201112 && !__GNUC_PREREQ (4,7))

I think this wants to be:

#if (!defined _Noreturn \
     && (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) < 201112 \
     &&  !__GNUC_PREREQ (4,7))