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

[Yutong Zhu via cfe-commits]

YutongZhuu wrote:

> This had the side effect of adding implicit-int-conversion warnings on e.g. the following code:
> 
> ```
> unsigned char foo(unsigned char x)
> {
>     return ~x;
> }
> ```
> 
> This seems correct, but this should probably be highlighted in the release notes.
> 
> Another example is:
> 
> ```
> unsigned int foo(unsigned char x)
> {
>     return ~(1<<x);
> }
> ```

Hi, could you edit the release note for me? I don't have write access, so I would have to submit a PR to do so. I don't think a PR with changes only in the release notes is a great idea.

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