[clang] [Clang] disallow # operators in attribute argument lists (PR #147308)

[Oleksandr T. via cfe-commits]

a-tarasyuk wrote:

@erichkeane @AaronBallman Thanks — it seems the changes will need to be revisited based on further guidance from WG21. Would it make sense to close this PR for now?


https://github.com/llvm/llvm-project/pull/147308