print-rtl.c: Use rtx_insn for various debug_ functions

print-rtl.c: Use rtx_insn for various debug_ functions

gcc/
	* rtl.h (debug_rtx_list): Strengthen param 1 "x" from const_rtx to
	const rtx_insn *.
	(debug_rtx_range): Likewise for params 1 and 2 "start" and "end".
	(debug_rtx_find): Likewise for param 1 "x".

	* print-rtl.c (debug_rtx_list): Strengthen param 1 "x" from
	const_rtx to const rtx_insn *.  Likewise for local "insn".
	(debug_rtx_range): Likewise for params 1 and 2 "start" and "end".
	(debug_rtx_find): Likewise for param 1 "x".
	(print_rtl): Likewise for local "tmp_rtx", adding a checked cast
	from const_rtx to const rtx_insn * within the appropriate cases of
	the switch statement.

	* config/rs6000/rs6000.c (rs6000_debug_legitimize_address):
	Strengthen local "insns" from rtx to rtx_insn * since this is
	passed to a call to debug_rtx_list.

From-SVN: r214362