Add chibicc

This program popped up on Hacker News recently. It's the only modern
compiler I've ever seen that doesn't have dependencies and is easily
modified. So I added all of the missing GNU extensions I like to use
which means it might be possible soon to build on non-Linux and have
third party not vendor gcc binaries.

libc/log/err.c

@@ -19,7 +19,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/log/bsd.h"
 
-noreturn void(err)(int eval, const char *fmt, ...) {
+wontreturn void(err)(int eval, const char *fmt, ...) {
   va_list va;
   va_start(va, fmt);
   (verr)(eval, fmt, va);