tree-optimization/117502 - VMAT_STRIDED_SLP vs VMAT_ELEMENTWISE when considering...

tree-optimization/117502 - VMAT_STRIDED_SLP vs VMAT_ELEMENTWISE when considering gather

The following treats both the same when considering to use gather or
scatter for single-element interleaving accesses.

This will cause

FAIL: gcc.target/aarch64/sve/sve_iters_low_2.c scan-tree-dump-not vect "LOOP VECTORIZED"

where we now vectorize the loop with VNx4QI, I'll leave it to ARM folks
to investigate whether that's OK and to adjust the testcase or to see
where to adjust things to make the testcase not vectorized again.  The
original fix for which the testcase was introduced is still efffective.

	PR tree-optimization/117502
	* tree-vect-stmts.cc (get_group_load_store_type): Also consider
	VMAT_STRIDED_SLP when checking to use gather/scatter for
	single-element interleaving access.
	* tree-vect-loop.cc (update_epilogue_loop_vinfo): STMT_VINFO_STRIDED_P
	can be classified as VMAT_GATHER_SCATTER, so update DR_REF for
	those as well.