[Bug c++/64961] nested template implementation crossing namespace fails with access error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64961

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And I think the code is invalid. If you want to define the function, don't use
a protected access path.