[Bug c++/77561] Unclear diagnostic for invalid declaration of partial specialization as friend

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77561

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #0)
> The user is not trying to declare a specialization, they're trying to define
> a friend. The error should tell them that is allowed,

Oops, should tell them that is **not** allowed.