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

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

1 nit on the release note, else this LGTM.

We still need to let Aaron decide how long we are going to give WG21 a chance to change this :) 

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