[lld] [llvm] [lld][MachO] Follow-up to use madvise() for threaded file page-in. (PR #157917)

[John Holdsworth via llvm-commits]

johnno1962 wrote:

@aganea, I've removed all the #if which were intended to show clearly where the new code paths are; In practice you can tell by looking for `if (config->readWorkers)` anyway. I've added use of llvm_is_multithreaded() instead of another couple of `#if`s . The current state of this minor PR should address the failures raised in the [other thread](https://github.com/llvm/llvm-project/pull/147134#discussion_r2337246489) but we won't know until it merges whether that is the case.

https://github.com/llvm/llvm-project/pull/157917