[Bug c++/83469] union is not accepted as a valid class-key in template name resolution

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83469

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #1)
> (gdb) p type
> $4 = <typename_type 0x7ffff0035348 U>
> (gdb) p class_key
> $5 = union_type
> 
> Should we allow such a combination?

Yes. The code change here will also fix PR 93809.
Let me try to see if I can fix it correctly.