tree-optimization/101756 - avoid vectorizing boolean MAX reductions

tree-optimization/101756 - avoid vectorizing boolean MAX reductions

The following avoids vectorizing MIN/MAX reductions on bools which,
when ending up as vector(2) <signed-boolean:64> would need to be
adjusted because of the sign change.  The fix instead avoids any
reduction vectorization where the result isn't compatible
to the original scalar type since we don't compensate for that
either.

2021-08-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101756
	* tree-vect-slp.c (vectorizable_bb_reduc_epilogue): Make sure
	the result of the reduction epilogue is compatible to the original
	scalar result.

	* gcc.dg/vect/bb-slp-pr101756.c: New testcase.