re PR c++/19891 (Covariant returns are broken)

re PR c++/19891 (Covariant returns are broken)

cp:
	PR c++/19891
	* class.c (build_simple_base_path): Build the component_ref
	directly.
	(update_vtable_entry_for_fn): Walk the covariant's binfo chain
	rather than using lookup_base.
	* search.c (dfs_walk_once): Add non-recursive assert check.
	* typeck.c (build_class_member_access_expr): It is possible for
	the member type to be both const and volatile.
testsuite:
	PR c++/19891
	* g++.dg/abi/covariant4.C: New.

From-SVN: r95005