hw-doloop: Use rtx_insn (touches config/bfin/bfin.c)

hw-doloop: Use rtx_insn (touches config/bfin/bfin.c)

gcc/
	* hw-doloop.h (struct hwloop_info_d): Strengthen fields
	"last_insn", "loop_end" from rtx to rtx_insn *.

	* hw-doloop.c (scan_loop): Likewise for local "insn".
	(discover_loop): Likewise for param "tail_insn".
	(discover_loops): Likewise for local "tail".

	* config/bfin/bfin.c (hwloop_optimize): For now, add a checked
	cast to rtx_insn * when assigning from an rtx local to a
	hwloop_info's "last_insn" field.

From-SVN: r214334