vect: Fix ICE in vectorizable_comparison PR93292

vect: Fix ICE in vectorizable_comparison PR93292

The following testcase ICEs on powerpc64le-linux.  The problem is that
get_vectype_for_scalar_type returns NULL, and while most places in
tree-vect-stmts.c handle that case, this spot doesn't and punts only
if it is non-NULL, but with different number of elts than expected.

2020-01-17  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/93292
	* tree-vect-stmts.c (vectorizable_comparison): Punt also if
	get_vectype_for_scalar_type returns NULL.

	* g++.dg/opt/pr93292.C: New test.