Create integrated assembler for chibicc

All we need now to complete the triforce is an integrated linker. That
way Cosmpolitan will let C be a "build anywhere run anywhere" language.

third_party/chibicc/chibicc.main.c

@@ -0,0 +1,5 @@
+#include "third_party/chibicc/chibicc.h"
+
+int main(int argc, char **argv) {
+  return chibicc(argc, argv);
+}