go-gcc.cc (Gcc_backend::set_placeholder_struct_type): Use build_distinct_type_copy rather than build_variant_type_copy.

	* go-gcc.cc (Gcc_backend::set_placeholder_struct_type): Use
	build_distinct_type_copy rather than build_variant_type_copy.
	(Gcc_backend::set_placeholder_array_type): Likewise.
	(Gcc_backend::named_type): Add special handling for builtin
	basic types.

From-SVN: r182698