Use backend interface for named types and array types.

Use backend interface for named types and array types.

	* go-gcc.cc (Gcc_backend::struct_type): Call fill_in_struct.
	(Gcc_backend::fill_in_struct): New function.
	(Gcc_backend::array_type): Implement.
	(Gcc_backend::fill_in_array): New function.
	(Gcc_backend::placeholder_pointer_type): New function.
	(Gcc_backend::set_placeholder_pointer_type): New function.
	(Gcc_backend::set_placeholder_function_type): New function.
	(Gcc_backend::placeholder_struct_type): New function.
	(Gcc_backend::set_placeholder_struct_type): New function.
	(Gcc_backend::placeholder_array_type): New function.
	(Gcc_backend::set_placeholder_array_type): New function.
	(Gcc_backend::named_type): New function.
	(Gcc_backend::circular_pointer_type): New function.
	(Gcc_backend::is_circular_pointer_type): New function.

From-SVN: r173380