re PR c++/22604 (ICE after invalid covariant return)

re PR c++/22604 (ICE after invalid covariant return)

cp:
	PR c++/22604
	* class.c (update_vtable_entry_for_fn): Don't process invalid
	covariant overriders.

	PR c++/23118
	* cp-tree.h (add_method): Add return value.
	* class.c (add_method): Return success indicator.
	* semantics.c (finish_member_declaration): Don't add an invalid
	method to the method list.
testsuite:
	PR c++/23118
	* g++.dg/overload/error2.C: New.

	PR c++/22604
	* g++.dg/inherit/covariant14.C: New.

From-SVN: r105549