middle-end/107115 - avoid bogus redundant store removal during RTL expansion

middle-end/107115 - avoid bogus redundant store removal during RTL expansion

The following preserves the (premature) redundant store removal
done in store_expr by appropriately guarding it with
mems_same_for_tbaa_p.  The testcase added needs scheduling disabled
for now since there's a similar bug there still present.

	PR middle-end/107115
	* expr.cc (store_expr): Check mems_same_for_tbaa_p before
	eliding a seemingly redundant store.

	* gcc.dg/torture/pr107115.c: New testcase.