[Bug c++/91428] Please warn on if constexpr (std::is_constant_evaluated())

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91428

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Well, but perhaps the right fix is removing "std::is_constant_evaluated ()"
instead?