[clang] [Sema] Support negation/parens with __builtin_available (PR #111439)

[Damyan Pepper via cfe-commits]

damyanp wrote:

> Hey Damyan, GH suggested you as a reviewer for this. Would you be able to TAL? Happy to find someone else if not :)

I'm not sure why GH would have done that, I'm afraid I wouldn't be able to give an informed review here. (I might have a quick look anyway).

https://github.com/llvm/llvm-project/pull/111439