Transparent sizeof.

(* Specifications: *)
Lemma data_at_singleton_array {cs} sh t vl v p:
vl = [v] ->
@data_at cs sh t v p |-- @data_at cs sh (tarray t 1) vl p.
Lemma data_at_singleton_array_inv {cs} sh t (vl : list (reptype t)) v p:
vl = [v] ->
@data_at cs sh (tarray t 1) vl p |-- @data_at cs sh t v p.