[clang] [Clang] Force expressions with UO_Not to not be non-negative (PR #126846)

[Jan Patrick Lehr via cfe-commits]

jplehr wrote:

> Hi, I think this broke two of our buildbots -- for reasons I don't quite understand, but reverting fixed the issue locally. Can you please take a look at it?
> 
> https://lab.llvm.org/buildbot/#/builders/10/builds/980 https://lab.llvm.org/buildbot/#/builders/73/builds/14304

I realized that `libc` compiles with `-Werror` and it appears that ours are the only libc bots that are affected.
So, I guess, the issue is on our end. Thank you.

https://github.com/llvm/llvm-project/pull/126846