d: Build TYPE_DECLs for non-numeric enum types.

d: Build TYPE_DECLs for non-numeric enum types.

This is done so that the DWARF pass will emit a DW_TAG_typedef where the
member type of an enum can't be represented in an ENUMERAL_TYPE.

gcc/d/ChangeLog:

	* d-builtins.cc (d_build_d_type_nodes): Call build_ctype() on all
	basic front-end types.
	* decl.cc (DeclVisitor::visit (EnumDeclaration *)): Always add decl to
	current binding level.
	(build_type_decl): Build TYPE_DECL as a typedef if not for an enum or
	record type.
	* types.cc (TypeVisitor::visit (TypeEnum *)): Set underlying type for
	ENUMERAL_TYPEs.  Build TYPE_DECL for non-numeric enums.