lower-subreg.c: Include rtl-iter.h.

lower-subreg.c: Include rtl-iter.h.

gcc/
	* lower-subreg.c: Include rtl-iter.h.
	(resolve_subreg_use): Turn from being a for_each_rtx callback
	to being a function that examines each subrtx itself.  Remove
	handling of null rtxes.
	(resolve_reg_notes, resolve_simple_move): Update accordingly.
	(decompose_multiword_subregs): Likewise.

From-SVN: r214647