[Bug c++/95703] New: Please backport 0998d2fd59e7a5eb3a3566c57625702bbdc6a05f to gcc 9

[rafael at espindo dot la]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95703

            Bug ID: 95703
           Summary: Please backport
                    0998d2fd59e7a5eb3a3566c57625702bbdc6a05f to gcc 9
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rafael at espindo dot la
                CC: jason at redhat dot com
  Target Milestone: ---

We (seastar) recently hit a build error with gcc 9 because the fix in
0998d2fd59e7a5eb3a3566c57625702bbdc6a05f is missing.

Given that P1286R2 is about c++11 and newer, could the fix be backported to gcc
9?

The original commit message is:

    Implement P1286R2, Contra CWG1778

    The C++11 requirement that an explicit exception-specification on a
    defaulted function match the implicit one was found to be problematic for
    std::atomic.  This paper, adopted in February, simply removes that
    requirement: if an explicitly defaulted function has a different
    exception-specification, that now works just like a user-written function:
    either it isn't noexcept when it could be, or it is noexcept and will call
    terminate if an exception is thrown.