Function check_intrinsic_arg_count 

fn check_intrinsic_arg_count<'a, 'tcx, const N: usize>(
    args: &'a [OpTy<'tcx>],
) -> InterpResult<'tcx, &'a [OpTy<'tcx>; N]>
where
    &'a [OpTy<'tcx>; N]: TryFrom<&'a [OpTy<'tcx>]>,

Check that the number of args is what we expect.