tree-optimization/119586 - aligned access to unaligned data

tree-optimization/119586 - aligned access to unaligned data

The following reverts parts of r15-8047 which assesses alignment
analysis for VMAT_STRIDED_SLP is correct by using aligned accesses
where allowed by it.  As the PR shows this analysis is still incorrect,
so revert back to assuming we got it wrong.

	PR tree-optimization/119586
	* tree-vect-stmts.cc (vectorizable_load): Assume we got
	alignment analysis for VMAT_STRIDED_SLP wrong.
	(vectorizable_store): Likewise.

	* gcc.dg/vect/pr119586.c: New testcase.