[Bug c++/109340] Inconsistent diagnostics for invalid member types in union

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109340

--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:31a909712014b75fc6ae2ca5eaa425f218bb5f32

commit r13-6934-g31a909712014b75fc6ae2ca5eaa425f218bb5f32
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Mar 29 22:16:55 2023 +0100

    libstdc++: Use std::remove_cv_t in std::optional::transform [PR109340]

    We need to strip cv-qualifiers from the result of the callable passed to
    std::optional::transform.

    For std::expected::transform and std::expected::transform_error I
    noticed we were stripping cv-qualifiers but were also incorrectly
    stripping references.

    libstdc++-v3/ChangeLog:

            PR libstdc++/109340
            * include/std/expected (expected::transform): Use
            std::remove_cv_t instead of std::remove_cvref_t.
            (expected::transform_error): Likewise.
            (expected<cv void, E>::transform): Likewise.
            (expected<cv void, E>::transform_error): Likewise.
            * include/std/optional (transform): Use std::remove_cv_t.
            * testsuite/20_util/optional/monadic/pr109340.cc: New test.