[llvm] [docs] Check for absolute self-documentation links (PR #222504)

[Reid Kleckner via llvm-commits]

rnk wrote:

> (Fyi, I’m the wrong person to add as a reviewer when it comes to reviewing Python code because I barely know any Python)

Yeah, sorry, I think I wanted to list you as the reviewer for the clang-side changes only, but I got this result.

https://github.com/llvm/llvm-project/pull/222504