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

[Richard Smith via cfe-commits]

zygoloid wrote:

Can you update the first comment on this PR to reflect what you want to be in the commit message? I notice that it doesn't describe what you're doing with negation yet. Thanks!

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