[llvm] Use zlib cmake target rather than variables (PR #90322)

[Andrew Marshall via llvm-commits]

planetmarshall wrote:


> 
> But given this simplifies the code - that seems appealing.
> But what's the cost, if any? Does this break some existing users/use cases?

Hi David, thanks for the comment. This should not break any existing use cases, but I want to run a few more tests to be sure before pinging a reviewer.



https://github.com/llvm/llvm-project/pull/90322