message: concepts: Use clang flavor of requires_ with MSVC
diff: @@ -783,7 +783,7 @@ namespace concepts
  return true;
  }
  -#ifdef __clang__
  +#if defined(__clang__) || defined(_MSC_VER)
  template<bool B>
  ::concepts::detail::enable_if_t<void, B> requires_()
  {}
  