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

[Balázs Benics via cfe-commits]

https://github.com/steakhal commented:

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?

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