Error "Function is not implememt" for override functions

#include <iostream>

struct BaseClass {
  virtual ~BaseClass() {}

  virtual void M ()  __attribute__((nothrow)) {
    std::cout << "base" << std::endl;
  }
};


class DerivedClass final : public BaseClass {

 public:
  virtual ~DerivedClass() {}

  void M() override __attribute__((nothrow)) {
    std:: cout << "derived x" << std::endl;
  }

};

int main() {
  DerivedClass d;
  d.M();
  return 0;
}

I have the above code, CLion reports error "Function M is not implememt". However I can compile and run the program correctly. I cannot change my code because the code is an extraction from a large project where all override functions are declared in the format of "override __attribute__((...))".

How do I make CLion inspection reporting errors consistent with the compiler?