[PATCH] libstdc++: Implement P2328 changes to join_view

[Tim Song]

On Fri, Apr 30, 2021 at 12:11 PM Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> +       template<typename _Iter>
> +         _Tp&
> +         _M_emplace_deref(const _Iter& __i)
> +         {
> +           this->reset();
> +           return this->emplace(*__i);
> +         }

This incurs a move, avoiding of which is the sole reason for
emplace-deref's existence.

> +      };
> +  }
> +