This makes the mapping between iOS & tvOS/watchOS versions more accurate. For example, iOS 9.3 now gets correctly mapped into tvOS 9.2 and not tvOS 9.3.
Before this change, the incorrect mapping could cause excessive or missing warnings for code that specifies availability for iOS, but not for tvOS/watchOS.
rdar://81491680
Differential Revision: https://reviews.llvm.org/D116822
Egor Zhdan