[Bug c++/67139] [concepts] ICE on checking concepts with void

[eric.niebler at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67139

--- Comment #2 from Eric Niebler <eric.niebler at gmail dot com> ---
Thanks, except that that is invalid code, and this bug is an ICE-on-valid.
Here's the equivalent valid repro case:

template <class T>
constexpr typename T::type::value_type _v = T::type::value;

template <class T> concept bool IsTrue_() { return _v<T>; }

template <class T> concept bool Unpossible() {
  return IsTrue_<T &&>();
}

template <class> constexpr bool unpossible() { return false; }
Unpossible{ T }
constexpr bool unpossible() { return true; }

static_assert((!unpossible<void>()), "");