Coroutines are not supported by C-generating back end #179

//options_all:--c++20
#include <coroutine>

struct task {
  struct promise_type {
    task get_return_object() { return {}; }
    std::suspend_never initial_suspend() { return {}; }
    std::suspend_never final_suspend() noexcept { return {}; }
    void return_void() {}
    void unhandled_exception() {}
  };
};

task f() { co_return; }