Method await_ready

tests/Issue526.cpp:11–11

struct executable { static U execute() { co_await T{}; } };
struct hello_logic  {
    bool await_ready() const noexcept { return true; }
    void await_suspend(std::coroutine_handle<>) const noexcept { }
    void await_resume() const noexcept { std::cout << "Hello, world" << std::endl; }
};