https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113644
--- Comment #4 from Sam James <sjames at gcc dot gnu.org> ---
cvise gave me:
```
template <class _Cp, bool = _Cp ::value> class __bit_reference;
template <class _Cp> struct __bit_reference<_Cp, false> {
class __bit_reference<_Cp>;
};
```
gcc doesn't warn on it, but clang does
