fn univariant_uninterned<'tcx>(
    cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
    ty: Ty<'tcx>,
    fields: &[TyAndLayout<'_>],
    repr: &ReprOptions,
    kind: StructKind
) -> Result<LayoutS<VariantIdx>, LayoutError<'tcx>>