std.process.Child: implement maxrss on Darwin

Notably the Darwin (XNU) kernel the maxrss field is number of bytes
and not kilobytes (kibibytes) like other platforms (e.g. Linux, BSD).

watchOS and tvOS are not supported because they do not have the ability
to spawn a child process. iOS is enabled but due to OS sandboxing it
should fail with a permission error.
f6a2b72ba8tjog committed on 3/25/2023, 2:20:50 AM· committed by Jakub Konkaparentf99b753
2 files changedLine totals unavailable