[Bug libstdc++/79980] Possible bug in codecvt.cpp bitmask setting code

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79980

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Apparently so is min vs max:

    maxcode = std::max(max_single_utf16_unit, maxcode);