1) Качаем Xcode 5.1.1 с портала Apple,
2) Запускаем скачаный образ,
3) Запускаем Terminal:
sudo cp -r /Volumes/Xcode/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS7.1.sdk /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/