[Bug c++/82478] Rejects valid access to private member type that should be allowed by friend

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82478

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The template argument list of ::HasPrivate<T, void_t<typename T::PRIVATE>> is
not a base-specifier.