[clang] [clang][docs] Fix docs-clang-html. (PR #142387)

[Abid Qadeer via cfe-commits]

abidh wrote:

I see that https://clang.llvm.org/docs/DiagnosticsReference.html#wunique-object-duplication is showing this correctly without this PR so problem may be something local to my machine. Closing it for now.

https://github.com/llvm/llvm-project/pull/142387