[Bug libstdc++/110708] std::format("{:%EEC %OOd}", std::chrono::system_clock::now()) should be rejected

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110708

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And similarly for %OEy and %EOy