[Bug c++/91264] modifying const-qual object in constexpr context not detected

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91264

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Similar for e.g.
  const_cast<int &>(i)++;