[clang] Clean up strange uses of getAnalysisIfAvailable (PR #65729)

[Jay Foad via cfe-commits]

jayfoad wrote:

> I guess I don't know how pull requests and reviewing works in github. I actually added 3 comments on this patch a several days (or weeks) ago. But turns out that they were "pending" because I had only "started review" and not found the place to "submit review".

For that reason I usually click "add single comment" instead of "start a review".

https://github.com/llvm/llvm-project/pull/65729