Hint Resolve areg_sound aregs_sound: va.

Lemma abuiltin_arg_sound:
forall bc ge rs sp m ae rm am,
ematch bc rs ae ->
romatch bc m rm ->
mmatch bc m am ->
genv_match bc ge ->
bc sp = BCstack ->
forall a v,
eval_builtin_arg ge (fun r => rs#r) (Vptr sp Ptrofs.zero) m a v ->
vmatch bc v (abuiltin_arg ae am rm a).