IF you are here because you updated your device (iPhone, Apple TV etc) and can no longer export your apps to this updated device, there is a workaround!
You can actually copy the newest version of iOS XCode SDK from a newer version of XCode into your older version of XCode.
1
Rename your old XCode.app to XCode7.app, and install the latest version of XCode (yes you can have multiple versions)
2
Grab the folder in your new XCode package content folder:
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/10.3\
And add it in the same place of your XCode 7.3 or 8.2 version
/Applications/Xcode7.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/
Restart XCode and you will be able to keep working!