[clang] [Clang] raise extension warning for unknown namespaced attributes (PR #120925)

[Oleksandr T. via cfe-commits]

a-tarasyuk wrote:

@erichkeane @AaronBallman @cor3ntin, just checking if there are any updates on this, as the `Clang 20` release was landed.



https://github.com/llvm/llvm-project/pull/120925