Function emit_aapcs_va_arg 

fn emit_aapcs_va_arg<'ll, 'tcx>(
    bx: &mut GenericBuilder<'_, 'll, FullCx<'ll, 'tcx>>,
    list: OperandRef<'tcx, Value<'ll>>,
    layout: TyAndLayout<'tcx>,
) -> Value<'ll>