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

[Oleksandr T. via cfe-commits]

a-tarasyuk wrote:

@AaronBallman I’ve moved the diagnostic under the `-Wattribute-preprocessor-tokens` warning flag and made it a `pedantic` diagnostic, which will be triggered in C++. Is that the behavior you were aiming for?

@cor3ntin should `/` be disallowed as well, or are `#` and `/` the only tokens that need to be blocked, with `##` remaining valid?



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