lower-subreg.c: Use rtx_insn

lower-subreg.c: Use rtx_insn

gcc/
	* lower-subreg.c (simple_move): Strengthen param "insn" from rtx
	to rtx_insn *.
	(resolve_reg_notes): Likewise.
	(resolve_simple_move): Likewise for return type, param "insn", and
	locals "insns", "minsn".
	(resolve_clobber): Strengthen param "insn" from rtx to rtx_insn *.
	(resolve_use): Likewise.
	(resolve_debug): Likewise.
	(find_decomposable_shift_zext): Likewise.
	(resolve_shift_zext): Likewise for return type, param "insn", and
	locals "insns", "in".  Eliminate use of NULL_RTX in favor of NULL.
	(decompose_multiword_subregs): Likewise for local "insn",
	"orig_insn", "decomposed_shift", "end".

From-SVN: r214346