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.

dsp/mpeg/mp2.c

@@ -266,7 +266,7 @@ struct plm_audio_t {
 	float D[1024];
 	float V[1024];
 	float U[32];
-} aligned(64);
+} forcealign(64);
 
 typedef plm_audio_t plm_audio_t;