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.

tool/net/redbean.c

@@ -353,7 +353,7 @@ static const char *GetContentType(const char *path, size_t n) {
   }
 }
 
-static noreturn void PrintUsage(FILE *f, int rc) {
+static wontreturn void PrintUsage(FILE *f, int rc) {
   fprintf(f, "SYNOPSIS\n\n  %s%s", program_invocation_name, USAGE);
   exit(rc);
 }