lavc: add ffwavesynth pseudo-codec.

libavcodec/allcodecs.c

@@ -265,6 +265,7 @@ void avcodec_register_all(void)
     REGISTER_ENCDEC  (DCA, dca);
     REGISTER_DECODER (DSICINAUDIO, dsicinaudio);
     REGISTER_ENCDEC  (EAC3, eac3);
+    REGISTER_DECODER (FFWAVESYNTH, ffwavesynth);
     REGISTER_ENCDEC  (FLAC, flac);
     REGISTER_ENCDEC  (G723_1, g723_1);
     REGISTER_DECODER (G729, g729);