CFLAA: return MustAlias when pointers p, q are equal, i.e.,

must-alias(p, sz_p, p, sz_q)  irrespective of access sizes sz_p, sz_q

As discussed a couple of weeks ago on the ML.
This makes the behavior consistent with that of BasicAA.
AA clients already check the obj size themselves and may not require the
obj size to match exactly the access size (e.g., in case of store forwarding)

llvm-svn: 310495