I have downloaded a legacy swift app using git and run
git add -A
Xcode 8 compiles against the iOS 10 SDK. This differs slightly from the iOS 9 SDK and thus the errors. You won't be able to use Xcode 8 with Swift 2.2 code.
If you look at the Alamofire branches, https://github.com/Alamofire/Alamofire/branches, you'll see work on 2.3 and 3.0 compatibility.
Also, read this thread for details on how to use those branches: https://github.com/Alamofire/Alamofire/issues/1312.