Only import darwin on platforms which support it. Otherwise fallback to the appropriate C stdlib library
Only import darwin on platforms which support it. Otherwise fallback to
the appropriate C stdlib library

Radar-Id: rdar://problem/88578177

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