[Bug c++/88242] static_assertion only fires when class is templated

[fiesh at zefix dot tv]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88242

--- Comment #2 from fiesh at zefix dot tv ---
So from the discussion

https://bugs.llvm.org/show_bug.cgi?id=41785

I think this also is actually ill-formed code.