[Bug c++/61457] [C++11/14 only] Inaccurately refusing non-ODR usage of type with no linkage

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61457

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
In C++17 the static member is implicitly inline, so GCC no longer expects it to
have a separate definition.