Implement C++0x unrestricted unions (N2544)
* class.c (check_field_decl): Loosen union handling in C++0x.
* method.c (walk_field_subobs): Split out from...
(synthesized_method_walk): ...here. Set msg before loops.
(process_subob_fn): Check for triviality in union members.
* init.c (sort_mem_initializers): Splice out uninitialized
anonymous unions and union members.
(push_base_cleanups): Don't automatically destroy anonymous unions
and union members.