[Bug c++/68089] c++ friend with template

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68089

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The error seems correct to me, the function is only a friend of its first
argument, not its second. Friendship is not transitive, just because the
function friends with C<T> and C<T> is friends with C<U> that does not mean the
function is friends with C<U>.