[Bug libstdc++/120446] [C++23] Implement P2655R3 common_reference_t of reference_wrapper Should Be a Reference Type

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120446

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-15 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:95f5abd112020f86aba51ed35a6d517fb09682fe

commit r15-10609-g95f5abd112020f86aba51ed35a6d517fb09682fe
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Dec 5 13:43:26 2025 -0500

    libstdc++: Consolidate bullet 1 __common_reference_impl partial specs

    ... and in passing use requires-clauses instead of void_t based SFINAE.
    This is a non-functional change that'll simplify implementing the
    P2655R3 change to common_reference.

            PR c++/120446

    libstdc++-v3/ChangeLog:

            * include/std/type_traits (__common_reference_impl): Rewrite
            partial specializations to use requires-clause instead of
            an additional void_t template parameter.  Consolidate the
            partial specializations corresponding to bullet 1.

    Reviewed-by: Tomasz KamiÅski <tkaminsk@redhat.com>
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
    (cherry picked from commit cbdbbdd1fccfd789e6fbcb37b1b602bb7482de4b)