Function bad_non_zero_sized_fields

fn bad_non_zero_sized_fields<'tcx>(
    tcx: TyCtxt<'tcx>,
    adt: AdtDef<'tcx>,
    field_count: usize,
    field_spans: impl Iterator<Item = Span>,
    sp: Span,
)

Emit an error when encountering two or more non-zero-sized fields in a transparent enum.