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

[Daniel Rodríguez Troitiño via llvm-commits]

drodriguez wrote:

@zygoloid I found the existing discussion about why not only Linux in the comments of #152595. Makes sense.

The problem is that the default of `RequiresNullTerminator` makes all the simple invocations to `getFile`, even if being binaries, fall onto the slow path of not being mmapped, this is a change from the status quo before #152595. Trying to modify the default of `RequiresNullTerminator` will involve going through every callsite of `getFile` and figure out if the default was being used intentionally, or the default was just accidentally working.

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