[Bug libstdc++/111250] __glibcxx_requires_subscript assertions are not checked during constant evaluation

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111250

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on trunk. I think this would be good to backport so that we diagnose more
errors during constant evaluation.