Method push

tests/relacy/relacy/example/stack/stack.cpp:16–27

    }

    void push(int data)
    {
        rl::var<node*> n = new node ();
        n($)->data_($) = data;
        node* next = head_.load(rl::memory_order_relaxed);
        for (;;)
        {
            n($)->next_.store(next, rl::memory_order_relaxed);
            if (head_.compare_exchange_weak(next, n($), rl::memory_order_release))
                break;
        }
    }

    int pop()
    {