Correct a workaround for vectorized stores.

Correct a workaround for vectorized stores.

Resolves:
PR middle-end/96963 - -Wstringop-overflow false positive with -ftree-vectorize when assigning consecutive char struct members
PR middle-end/94655 - -Wstringop-overflow on implicit string assignment with vectorized char store

gcc/ChangeLog:

	PR middle-end/96963
	PR middle-end/94655
	* builtins.c (handle_array_ref): New helper.
	(handle_mem_ref): New helper.
	(compute_objsize_r): Factor out ARRAY_REF and MEM_REF handling
	into new helper functions.  Correct a workaround for vectorized
	assignments.

gcc/testsuite/ChangeLog:

	PR middle-end/96963
	PR middle-end/94655
	* gcc.dg/Wstringop-overflow-47.c: Xfail tests.
	* gcc.dg/Wstringop-overflow-65.c: New test.
	* gcc.dg/Warray-bounds-69.c: Same.