Not an opinion. It's just a fact.

For me this is over.

It doesn't compile in another compilers. For example try to compile it into Visual Studio C++

Also, the implementation it's not yours. You're using a builtin function that only the GCC compiler has implemented. So, I must say that it's only a nice trick. But must not be considered best practice by no means.

It's faster than other implementations (including mine)? YES
Has been implemented by you? NO
Must be considered a solution to the exercise? NO!