gcc/
	* doc/md.texi: Document the MIPS "v" constraint.
	* config/mips/mips.h (reg_class): Revert last change.
	(REG_CLASS_NAMES): Likewise.
	(REG_CLASS_CONTENTS): Likewise.
	* config/mips/mips.c (mips_regno_to_class): Likewise.
	* config/mips/constraints.md (v): Likewise, but add documentation.
	Add a comment to say that this constraint should not be used in
	gcc code.

From-SVN: r137734