[Bug c++/123297] GCC accepts class template deduction guide with alias return type instead of simple-template-id

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123297

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://cplusplus.github.io/CWG/issues/2292.html