[lld] [lld][MachO] Silence warnings about --read-workers parsing (PR #156608)

[John Holdsworth via llvm-commits]

johnno1962 wrote:

Thanks for picking this up @frederik-h. If this is giving a warning the code just after it for OPT_threads_eq should be as well as I copied it. Also, while you're changing at this code, perhaps the variable name should be "workers" not "threads".

https://github.com/llvm/llvm-project/pull/156608