Correctly detect legacy iOS simulator Mach-O objectfiles

The code in ObjectFileMachO didn't disambiguate between ios and
ios-simulator object files for Mach-O objects using the legacy
ambiguous LC_VERSION_MIN load commands. This used to not matter before
taught ArchSpec that ios and ios-simulator are no longer compatible.

rdar://problem/66545307

Differential Revision: https://reviews.llvm.org/D85358