[Bug c++/93807] -std=c++2a allows to omit out-of-class declaration in template class

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93807

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(Clang doesn't accept this code because it doesn't implement P0846R0 yet.)