Support for serialization of member types

Support for serialization of member types

cp/ChangeLog:

	* abi-instr.cc (gen_scope_of):  Member types are linked to their
	scope via their DECL_CONTEXT (TYPE_NAME()), not their
	TYPE_CONTEXT.  <grin/>.  Also, do not add empty elements to the
	scope hash table.
	(gen_scope_decl): Do not use a scope that is not yet fully built.
	We should not be using gen_scope_decl while building type or decl
	members.  Rather, we should just be sticking the members into the
	non-fully-built type/decl that we have at hand.
	(gen_class_type_in_scope): Handle member types.  Also, for member
	functions, use the new (more generic) version of
	abigail::add_decl_to_scope.

gcc/testsuite/ChangeLog:

	* g++.dg/abi-dump/bases-0.C.bi: Update this for member type(def).
	* g++.dg/abi-dump/simple-class-0.C.bi: Likewise.