var-tracking.c: Include rtl-iter.h.

var-tracking.c: Include rtl-iter.h.

gcc/
	* var-tracking.c: Include rtl-iter.h.
	(rtx_debug_expr_p): Turn from being a for_each_rtx callback
	to being a function that examines each subrtx itself.
	(use_type): Update accordingly.

From-SVN: r214661