message: don't crash with FN call that return aggregates
diff: @@ -1038,6 +1038,9 @@ StateValue FnCall::toSMT(State &s) const {
  }
  // FIXME: broken for functions that return aggregate types
  + if (getType().isAggregateType())
  + return {};
  +
  auto poison_name = fnName + "#poison";
  add_implies_axiom(poison_name);
  