[Bug c++/111018] lexical interpretation of friendship rules depends on whether the friend function has a definition

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111018

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So if we make a definition outside of the class:
```
  template <class Self>
  auto bar(Self s) -> decltype(::T::foo(s))
  {

  }
```
Then clang rejects the code too ...
So ....