Global Opaque Xarray.

Lemma Xarray_update:
forall i b,
length b = LBLOCK ->
(16 <= i < 64)%nat ->
upd_reptype_array tuint (Z.of_nat i mod 16)
(map Vint (Xarray b i))
(Vint (W (nthi b) (Z.of_nat i)))
= map Vint (Xarray b (i+1)).