[clang] [Clang] [NFC] Add release note about libstdc++ bug (PR #93059)

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Sirraide wrote:

> > This closes #92439.
> 
> It does not (`s++++` is still not diagnosed)

Oh, right; this was mainly in reference to the libstdc++ bug since that’s what’s most of the discussion on that issue has been about. I’d maybe suggest moving the `s++++` case to a different issue?

https://github.com/llvm/llvm-project/pull/93059