Fix remaining test issues
Fix remaining test issues

Needed to add availability information for macOS, iOS, and watchOS to
avoid emitting unintended errors on the `async` keyword.

gregomni/swift,glessard/swift,ahoppen/swift,glessard/swift,JGiola/swift,atrick/swift,ahoppen/swift,roambotics/swift,benlangmuir/swift,gregomni/swift,gregomni/swift,apple/swift,roambotics/swift,apple/swift,apple/swift,gregomni/swift,roambotics/swift,roambotics/swift,ahoppen/swift,roambotics/swift,apple/swift,rudkx/swift,roambotics/swift,JGiola/swift,ahoppen/swift,benlangmuir/swift,JGiola/swift,rudkx/swift,apple/swift,apple/swift,benlangmuir/swift,glessard/swift,rudkx/swift,glessard/swift,gregomni/swift,JGiola/swift,rudkx/swift,atrick/swift,benlangmuir/swift,glessard/swift,JGiola/swift,glessard/swift,rudkx/swift,benlangmuir/swift,atrick/swift,atrick/swift,atrick/swift,ahoppen/swift,atrick/swift,JGiola/swift,rudkx/swift,ahoppen/swift,benlangmuir/swift,gregomni/swift