Checking whether a function (not a method) exists in c++11 via templates

So with SFINAE and c++11, it is possible to implement two different template functions based on whether one of the template parameters can be substituted.

For example

struct Boo{
   void saySomething(){ cout << "Boo!" << endl; }
};

template<class X>
void makeitdosomething(decltype(&X::saySomething), X x){
   x.saySomething();
}

template<class X>
void makeitsaysomething(int whatever, X x){
    cout << "It can't say anything!" << endl;
}


int main(){
   makeitsaysomething(3);
   makeitsaysomething(Boo());
}

or something along that line.

My question is.. how does one do the same thing, but for non-member functions?

In particular I'm trying to check if there's such thing as an:

operator<<(std::ostream& os, X& whateverclass);

that exists. Is it possible to test it?