[llvm] Added YouTube resource link on LLVM build to CMAKE.rst (PR #108935)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I don't think we should be adding links to youtube videos to the docs. If there is valuable information in that 50 minute talk, then it should be included here in text form.

https://github.com/llvm/llvm-project/pull/108935