code: Env<GenContext> unwind(JCTree target, Env<GenContext> env) {
          Env<GenContext> env1 = env;
          while (true) {
              genFinalizer(env1);
              if (env1.tree == target) break;
              env1 = env1.next;
          }
          return env1;
      }
docs: Generate code to call all finalizers of structures aborted by
  a non-local
  exit.  Return target environment of the non-local exit.
  @param target      The tree representing the structure that's aborted
  @param env         The environment current at the non-local exit.