loop-iv.c: Include rtl-iter.h.

loop-iv.c: Include rtl-iter.h.

gcc/
	* loop-iv.c: Include rtl-iter.h.
	(find_single_def_src): New function.
	(replace_single_def_regs): Turn from being a for_each_rtx callback
	to being a function that examines each subrtx itself.
	(replace_in_expr, simplify_using_initial_values): Update accordingly.

From-SVN: r214645