[clang] [llvm] [CMake] Version Darwin dylib identities (PR #189004)

[Tamir Duberstein via llvm-commits]

tamird wrote:

Ah, please *do not* squash and merge. These commits are intentionally factored the way that they are; the first two are preparatory cleanup and only the last one introduces behavior change. If a revert is needed, best that only the last commit is reverted. I'd like to retain all the commit messages, please.

https://github.com/llvm/llvm-project/pull/189004