[Bug c++/58969] bogus error: the value of 'kName' is not usable in a constant expression

[richard-gccbugzilla at metafoo dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58969

--- Comment #2 from Richard Smith <richard-gccbugzilla at metafoo dot co.uk> ---
(In reply to Kai Tietz from comment #1)
> Hmm, issue seems to be in too restrictive decl_maybe_constant_var_p function.

I don't know how the GCC code is structured, but I don't think that's right;
that function appears to be checking whether the value of the variable can be
used in a constant expression. The relevant condition here is whether the
address of the variable can be used.