-mstring is only enabled by default on 601, and with -Os on some
configurations.  It is almost always slower (than not using it) and
does not very often lead to smaller code.

This patch disables it.  If a user uses -mstring he gets a warning
(but not with -mno-string).  I left the target attribute in place, it
just doesn't do anything anymore.

The patch also deletes a whole bunch of code.  The 'N' and 'O' output
modifiers are now unused, but now is not the time to delete them.


	* config/rs6000/predicates.md (load_multiple_operation): Delete.
	(store_multiple_operation): Delete.
	* config/rs6000/rs6000-cpus.def (601): Remove MASK_STRING.
	* config/rs6000/rs6000-protos.h (rs6000_output_load_multiple): Delete.
	* config/rs6000/rs6000-string.c (expand_block_move): Delete everything
	guarded by TARGET_STRING.
	(rs6000_output_load_multiple): Delete.
	* config/rs6000/rs6000.c (rs6000_option_override_internal): Delete
	OPTION_MASK_STRING / TARGET_STRING handling.
	(print_operand) <'N', 'O'>: Add comment that these are unused now.
	(const rs6000_opt_masks) <"string">: Change mask to 0.
	* config/rs6000/rs6000.h (TARGET_DEFAULT): Remove MASK_STRING.
	(MASK_STRING): Delete.
	* config/rs6000/rs6000.md (*mov<mode>_string): Delete TARGET_STRING
	parts.  Simplify.
	(load_multiple): Delete.
	(*ldmsi8): Delete.
	(*ldmsi7): Delete.
	(*ldmsi6): Delete.
	(*ldmsi5): Delete.
	(*ldmsi4): Delete.
	(*ldmsi3): Delete.
	(store_multiple): Delete.
	(*stmsi8): Delete.
	(*stmsi7): Delete.
	(*stmsi6): Delete.
	(*stmsi5): Delete.
	(*stmsi4): Delete.
	(*stmsi3): Delete.
	(movmemsi_8reg): Delete.
	(corresponding unnamed define_insn): Delete.
	(movmemsi_6reg): Delete.
	(corresponding unnamed define_insn): Delete.
	(movmemsi_4reg): Delete.
	(corresponding unnamed define_insn): Delete.
	(movmemsi_2reg): Delete.
	(corresponding unnamed define_insn): Delete.
	(movmemsi_1reg): Delete.
	(corresponding unnamed define_insn): Delete.
	* config/rs6000/rs6000.opt (mno-string): New.
	(mstring): Replace by deprecation warning stub.
	* doc/invoke.texi (RS/6000 and PowerPC Options): Delete -mstring.

From-SVN: r256598