code: void genFinalizer(Env<GenContext> env) {
          if (code.isAlive() && env.info.finalize != null)
              env.info.finalize.gen();
      }
docs: Generate code to invoke the finalizer associated with given
  environment.
  Any calls to finalizers are appended to the environments `cont' chain.
  Mark beginning of gap in catch all range for finalizer.