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;
 

dsp/mpeg/mpeg.h

@@ -77,12 +77,12 @@ struct plm_samples_t {
   double time;
   unsigned int count;
 #ifdef PLM_AUDIO_SEPARATE_CHANNELS
-  float left[PLM_AUDIO_SAMPLES_PER_FRAME] aligned(32);
-  float right[PLM_AUDIO_SAMPLES_PER_FRAME] aligned(32);
+  float left[PLM_AUDIO_SAMPLES_PER_FRAME] forcealign(32);
+  float right[PLM_AUDIO_SAMPLES_PER_FRAME] forcealign(32);
 #else
-  float interleaved[PLM_AUDIO_SAMPLES_PER_FRAME * 2] aligned(32);
+  float interleaved[PLM_AUDIO_SAMPLES_PER_FRAME * 2] forcealign(32);
 #endif
-} aligned(32);
+} forcealign(32);
 
 typedef struct plm_samples_t plm_samples_t;