[Bug c/121811] stdckdint.h fails to compile in C++26 mode in GCC 14

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121811

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Use a configure time test instead of a compile time one.