[Bug libstdc++/111589] Use relaxed atomic increment (but not decrement!) in shared_ptr

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111589

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #3)
> > src/c++98/ios_init.cc:  __gnu_cxx::__atomic_add_dispatch(&_S_refcount, 1);
> 
> I think there's a race here, independent of the ordering used for this
> increment.

That's now PR 111676, and my fix removes the use of __atomic_add_dispatch, so
it no longer matters for this PR.