Avoid PR72749 by not using unspecs

Avoid PR72749 by not using unspecs

Rather than using unspecs in doloop insns to stop combine creating
these insns, use legitimate_combined_insn.

	PR target/72749
	* combine.c (recog_for_combine_1): Set INSN_CODE before calling
	target legitimate_combined_insn.
	* config/rs6000/rs6000.c (TARGET_LEGITIMATE_COMBINED_INSN): Define.
	(rs6000_legitimate_combined_insn): New function.
	* config/rs6000/rs6000.md (UNSPEC_DOLOOP): Delete, and remove
	all uses.
	(ctr<mode>_internal3): Rename from *ctr<mode>_internal5.
	(ctr<mode>_internal4): Rename from *ctr<mode>_internal6.
	(ctr<mode>_internal1, ctr<mode>_internal2): Remove '*' from name.

From-SVN: r244465