Make aliasing_component_refs_p to work harder when same_type_for_tbaa returns -1

	* tree-ssa-alias.c (aliasing_component_refs_p): Do not give up
	immediately after same_types_for_tbaa_p returns -1 and continue
	looking for possible exact match; if matching types are arrays
	watch for partial overlaps.
	(indirect_ref_may_alias_decl_p): Watch for partial array overlaps.
	(indirect_refs_may_alias_p): Do type based disambiguation first;
	update comment.

	* gcc.dg/lto/alias-access-path-2.0.c: New testcase.

From-SVN: r272036