c++: Refactor clone copying

c++: Refactor clone copying

This patch sets copy_fndecl_with_name to always inform
rest_of_decl_compilation that it is not a top-level decl (it's a
member function).  I also refactor build_cdtor_clones to conditionally
do the method vector updating.  That happens to be a better interface
for modules to use.

	gcc/cp/
	* class.c (copy_fndecl_with_name):  Always not top level.
	(build_cdtor_clones): Add update_methods parm, use it to
	conditionally update the method vec.  Return void
	(clone_cdtor): Adjust.
	(clone_constructors_and_destructors): Adjust comment.