You cannot obtain a pointer to a built-in operator. But fortunately, the standard library provides function objects for all standard operators. In your case, that object’s name is std::greater:
sort (arr, arr + N, std::greater<int>{});
Since C++14, you can even omit the argument type and it will be deduced from how the object is used:
sort (arr, arr + N, std::greater<>{});
And since C++17, the empty <> can be omitted too:
sort (arr, arr + N, std::greater{});