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/runtime/winmain.greg.c

@@ -119,7 +119,7 @@ static textwindows char *AllocateMemory(void *addr, size_t size, int64_t *h) {
       kNtNumaNoPreferredNode);
 }
 
-static textwindows noreturn void WinMainNew(void) {
+static textwindows wontreturn void WinMainNew(void) {
   int64_t h;
   size_t size;
   int i, count;