tree-optimization/115895 - overrun with masked loop

tree-optimization/115895 - overrun with masked loop

The following addresses the fact that with loop masking (or regular
mask loads) we do not implement load shortening but we override
the case where we need that for correctness.  Likewise when we
attempt to use loop masking to handle large trailing gaps we cannot
do so when there's this overrun case.

	PR tree-optimization/115895
	* tree-vect-stmts.cc (get_group_load_store_type): When we
	might overrun because the group size is not a multiple of the
	vector size we cannot use loop masking since that does not
	implement the required load shortening.

	* gcc.target/i386/vect-pr115895.c: New testcase.