[clang] [llvm] [docs] Replace clang.llvm.org/docs links with Sphinx links (PR #222507)

[Reid Kleckner via cfe-commits]

https://github.com/rnk commented:

PTAL, this has been updated since we landed the LLVM-side link checking. I think this is a positive change.

https://github.com/llvm/llvm-project/pull/222507