[llvm] [Github] Add lld to docs CI (PR #69821)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

There is a `lld` man page somewhere, but there doesn't seem to be a `docs-lld-man` target or anything equivalent. Is this something that's buildable?

https://github.com/llvm/llvm-project/pull/69821