* config/mmix/mmix.md: Change GNU CC to GCC in file header comment.
	* config/mmix/mmix.h: Ditto.
	* config/mmix/mmix-protos.h: Ditto.
	* config/mmix/mmix.c: Ditto.  Fix typo in comment.
	* config/mmix/mmix-modes.def: Change GNU CC to GCC in file header
	comment.  Comment extra CC modes.

From-SVN: r54869