rs6000.md (allocate_stack): Always use an update form instruction to update the stack...

rs6000.md (allocate_stack): Always use an update form instruction to update the stack back chain word...

	* config/rs6000/rs6000.md (allocate_stack): Always use an update
	form instruction to update the stack back chain word, even if the
	user has disabled the generation of update instructions.
	(movdi_<mode>_update_stack): New.
	(movsi_update_stack): Likewise.
	* config/rs6000/rs6000.c (rs6000_emit_allocate_stack): Likewise,
	always use an update form instruction to update the stack back
	chain word.

From-SVN: r144047