[clang] docs(clang): add some missing flags (PR #209519)

[Ehren Bendler via cfe-commits]

ebendler wrote:

> Is there a way to use these flags from `scan-build`? If yes, we should probably mention that. I think the llvm consensus is that new rst docs should disobey the 80 column rule and have each sentence in its own line. It play better with rewrites.
> 
> Could you post a picture of the generated html produced by the `docs-clang-html` target?

Thanks for the feedback, very helpful. Rendered pictures:

<img width="1440" height="1200" alt="clang-doc-preview" src="https://github.com/user-attachments/assets/8acafce8-6482-4eeb-b961-631f2f801b64" />
<img width="1530" height="1980" alt="clang-users-manual-render-06" src="https://github.com/user-attachments/assets/96d30148-e63b-49ca-b425-d840ca983cb8" />


https://github.com/llvm/llvm-project/pull/209519