[SEJeff]

That’s not a builtin, so wouldn’t it be:

   #include <old-man-shouting-at-clouds.h>

[obezyian]

And it's kinda old, so maybe

  #define _POSIX_C_SOURCE 1
  #include <old-man-shouting-at-clouds.h>

[SEJeff]

Well played good sir, well played