[Bug libstdc++/124852] std::chrono::time_zone misparses Zone UNTIL fields whose DAY uses the ON format (lastSun, Sun>=8, etc.)

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124852

--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-15 branch has been updated by Tomasz Kaminski
<[email protected]>:

https://gcc.gnu.org/g:f47d0c439c9cd90b78fa1c26710739ad5e2224c2

commit r15-11430-gf47d0c439c9cd90b78fa1c26710739ad5e2224c2
Author: Tomasz KamiÅski <[email protected]>
Date:   Wed May 13 09:17:47 2026 +0200

    libstdc++: Use on_month_day istream operator in ZoneInfo parsing.
[PR124852]

    This patch changes ZoneInfo parsing, to use operator>> for on_month_day
    directly, and removes on_day tag. The operator>>(istream&, on_month_day)
    is updated to not override on.month if the MONTH component is not present,
    and set failbit instead. This allows to use in >> on >> time, to parse
    MONTH DAY TIME.

    We also handle failure to parse day number N for Www>=N or Www<=N
    productions, by leaving the day part of input unchanged and setting
    failbit.

            PR libstdc++/124852

    libstdc++-v3/ChangeLog:

            * src/c++20/tzdb.cc (on_month_day::on_day_t, on_month_day::on_day):
            Remove.
            (operator>>(istream&, on_month_day::day_t&)): Inlined into...
            (operator>>(istream&, on_month_day)): Inlined on_month_day::on_day.
            Avoid modifying on.month if MONTH is not present. Report failure
            on failure to parse day for LessEq / GreaterEq.

    Reviewed-by: Jonathan Wakely <[email protected]>
    Signed-off-by: Tomasz KamiÅski <[email protected]>
    (cherry picked from commit 2451667193e4e00b49c4ef9d95c0a3a1aa955f82)