Add alias disambiguation for vectorizer load/store IFNs

Add alias disambiguation for vectorizer load/store IFNs

The following adds support for MASK_STORE, MASK_LOAD and friends
to call_may_clobber_ref_p and ref_maybe_used_by_call_p.  Since
they all use a special argument to specify TBAA they are not really
suited for fnspec handling thus the manual support.

	* tree-ssa-alias.cc (ref_maybe_used_by_call_p_1): Special-case
	store internal functions and IFN_MASK_LOAD, IFN_LEN_LOAD
	and IFN_MASK_LOAD_LANES.
	(call_may_clobber_ref_p_1): Special-case IFN_MASK_STORE,
	IFN_LEN_STORE and IFN_MASK_STORE_LANES.