cp:
	PR c++/20232
	* class.c (update_vtable_entry_for_fn): Don't crash on invalid
	covariancy.

	* cp-tree.g (THUNK_TARGET): Expand comment.
	* method.c (use_thunk): Make sure we also use the target, if that
	is a thunk.
testsuite:
	PR c++/20232
	* g++.dg/inherit/covariant12.C: New.

From-SVN: r95733