more SCEV cache clearing

This fixes two more places, in loop interchange and in the
vectorizer where the SCEV verifier sees stale entries.

2020-07-29  Richard Biener  <rguenther@suse.de>

	* tree-vectorizer.c (vectorize_loops): Reset the SCEV
	cache if we removed any SIMD UID SSA defs.
	* gimple-loop-interchange.cc (pass_linterchange::execute):
	Reset the scev cache if we interchanged a loop.