[Bug c/108796] GCC 13 accepts [[noreturn]] attribute without -std=c2x

[sam at gentoo dot org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108796

--- Comment #2 from Sam James <sam at gentoo dot org> ---
Sorry, for completeness, I meant to include:
```
$ gcc-12 -O2 /tmp/foo.c # ditto with -std=c89
/tmp/foo.c:3:1: warning: 'noreturn' attribute ignored [-Wattributes]
    3 | [[noreturn]] void foo(void) {
      | ^
``