title: Xamarin UIStackView before iOS 9
body: <p>I have a Xamarin with Visual Studio for Mac project going. I decided to build the UI using Xcode and it has been working very well. However when I added a stack view with four views in it, it gave me a "UIStackView before iOS 9" error upon building and running on Xamarin. Xcode is using iOS version 10.2 and Xamarin also. I made sure my simulator is also running 9.0 or above. I can't figure out what else to do! Has anyone else encountered this issue?   </p>