dse.c: Include rtl-iter.h.

dse.c: Include rtl-iter.h.

gcc/
	* dse.c: Include rtl-iter.h.
	(check_mem_read_rtx): Change void * parameter to real type.
	Remove return value.
	(check_mem_read_use): Fix comment.  Use FOR_EACH_SUBRTX_PTR instead of
	for_each_rtx.  Don't handle null rtxes.

From-SVN: r214635