[Bug libstdc++/107468] std::from_chars doesn't always round to nearest

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107468

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The limited backport would be good, I don't think we need to backport the trunk
sync though.