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.