Ruby

use of stdckdint.h

C23 is going to have this header. The industry is already moving
towards accepting it; OSes and compilers started to implement theirs.

Why not detect its presence and if any, prefer over other ways.

See also:

• https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2683.pdf
• https://reviews.freebsd.org/D41734
• https://reviews.llvm.org/D157331
• https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=8441841a1b985d68245954af1ff023db121b0635