tree-optimization/122885 - avoid re-using accumulator for some bool vectors

tree-optimization/122885 - avoid re-using accumulator for some bool vectors

When boolean vectors do not use vector integer modes we are not
set up to produce the partial epilog in a correctly typed way,
so avoid this situation.  For the integer mode case we are able
to pun things correctly, so keep that working.

	PR tree-optimization/122885
	* tree-vect-loop.cc (vect_find_reusable_accumulator): Reject
	mask vectors which do not use integer vector modes.
	(vect_create_partial_epilog): Assert the same.

	* gcc.dg/torture/pr122873.c: New testcase.