[Bug libstdc++/108976] codecvt for Unicode allows surrogate code points

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108976

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think it would be good to backport it, what do you think?