amend SLP reduction testcases

This amends SLP reduction testcases that currently trigger
vect_attempt_slp_rearrange_stmts eliding load permutations to
verify this is actually happening.

2020-09-30  Richard Biener  <rguenther@suse.de>

	* gcc.dg/vect/pr37027.c: Amend.
	* gcc.dg/vect/pr67790.c: Likewise.
	* gcc.dg/vect/pr92324-4.c: Likewise.
	* gcc.dg/vect/pr92558.c: Likewise.
	* gcc.dg/vect/pr95495.c: Likewise.
	* gcc.dg/vect/slp-reduc-1.c: Likewise.
	* gcc.dg/vect/slp-reduc-2.c: Likewise.
	* gcc.dg/vect/slp-reduc-3.c: Likewise.
	* gcc.dg/vect/slp-reduc-4.c: Likewise.
	* gcc.dg/vect/slp-reduc-5.c: Likewise.
	* gcc.dg/vect/slp-reduc-7.c: Likewise.
	* gcc.dg/vect/vect-reduc-in-order-4.c: Likewise.