[clang-tools-extra] [clang-tools-extra] Fix add_clang_library usage (PR #109321)

[Vassil Vassilev via cfe-commits]

https://github.com/vgvassilev approved this pull request.

This change looks good to me. Let’s wait some more time for other reviewers before merging this. 

https://github.com/llvm/llvm-project/pull/109321