[Bug c++/68423] override/final doesn't cause error in templated class without base

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68423

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
You get an error as soon as you instantiate the templates. I don't know if the
standard requires an error even for uninstantiated templates, but there are
LOTS of things g++ doesn't diagnose in uninstantiated templates.