[Bug c++/86608] [6/7/8/9 Regression] volatile variable is taken as a constexpr

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86608

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Hmm, but I'm not happy about the error it produces, better use
non_const_var_error somehow.