[llvm] [CMake] Enable CMP0179 alongside CMP0156 for deduplication on LLD (PR #116497)

[Raul Tambre via llvm-commits]

tambry wrote:

LLD bug has now been reported as https://github.com/llvm/llvm-project/issues/116669 and I've reworded the commit message to hopefully make the effect and intent of this change clearer. Please do have another look.

https://github.com/llvm/llvm-project/pull/116497