linux: system headers need __builtin_va_list (musl) – Cuik doesn’t predefine it

[chrischtel]

chris@cruzi Cuik 3$ bin/cuik tests/hello.c                                                                                                                                     git
Included from /home/chris/dev/contributions/Cuik/tests/hello.c:1
Included from /usr/include/stdio.h:26
ERROR[0000]: you asked for a type __builtin_va_list but didn't declare it.
   --> /usr/include/bits/alltypes.h:326:9
     |
  326| typedef __builtin_va_list va_list;
     |         ^~~~~~~~~~~~~~~~~
     |
chris@cruzi Cuik 1 3$      

when trying to compile a trivial program with #include <stdio.h>

NOTE: Void Linux (musl) had a few other compatiblity issues I could fix. This error appeared after I fixed them with PR