[v3 PATCH] PR libstdc++/89825

[Jonathan Wakely]

On 26/03/19 16:48 +0200, Ville Voutilainen wrote:
>Slight tweak, the condition for _M_valid and _Extra_visit_slot_needed
>is now in sync.
>
OK, thanks.

>
>    PR libstdc++/89825
>    Fix based on a suggestion by Antony Polukhin.
>    * include/std/variant (__never_valueless): New.
>    (_M_valid): Use it.
>    (_Extra_visit_slot_needed): New.
>    (_Multi_array): Use it.
>    (_S_apply_all_alts): Likewise.