[llvm] [CMake] Pass doc-related LLVM variables to external projects (PR #65531)

[Will Hawkins via llvm-commits]

hawkinsw wrote:

Migrated here from Phabricator. I hope that this was the right thing to do! Thanks @llvm-beanz and @petrhosek ! 

https://github.com/llvm/llvm-project/pull/65531