[llvm] [Docs] Fix broken LLVM doc pages (PR #68631)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> Did you test the changes locally? Looking at the doc I would think that it would expect a slug, ie `project:DeveloperPolicy.rst#adding-an-established-project-to-the-llvm-monorepo`, but maybe not?

I did test them locally and this fixes all the issues. Not sure exactly why this works. I did try the slug and couldn't get it to work, but maybe I wasn't doing it correctly.

https://github.com/llvm/llvm-project/pull/68631