message: fix failure to compile in debug mode
diff: @@ -251,7 +251,7 @@ public:
  RetTy visitReturnInst(llvm::ReturnInst &i) {
  if (i.getNumOperands() == 0) {
  - assert(i.getType().isVoidTy());
  + assert(i.getType()->isVoidTy());
  return make_unique<Return>(Type::voidTy, Value::voidVal);
  }
  PARSE_UNOP();
  