Move vrp_simplify_cond_using_ranges into the simplifier.

This static VRP routine does a simplification with casted conditions.  Add it
to the general simplfier, and continue to invoke if from the VRP folder.

	* tree-vrp.c (vrp_simplify_cond_using_ranges): Add return type and
	move to vr-values.c.
	(simplify_casted_conds): Move to vrp_folder class.
	(execute_vrp): Call via vrp_folder now.
	* vr-values.c (simplify_cond_using_ranges_1): Call simplify_casted_cond.
	(simplify_using_ranges::simplify_casted_cond): Relocate from tree-vrp.c.
	* vr-values.h (simplify_casted_cond): Add prototype.