[Bug c++/102168] -Wnon-virtual-dtor shouldn't fire for protected dtor in a class with a friend declaration

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102168

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The -Wnon-virtual-dtor warning is just dumb, that's why I added Clang's
-Wdelete-non-virtual-dtor which should be used instead.