This makes sure to get a truth type for scatter masks even when they
are invariant.

2020-06-03  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/95487
	* tree-vect-stmts.c (vectorizable_store): Use a truth type
	for the scatter mask.

	* g++.dg/vect/pr95487.cc: New testcase.