title: Building a solution with Shared Project fails on references errors
body: <p>I have solution with UI Tests for my mobile applications in Xamarin. </p>
  
  <p>This is setup:</p>
  
  <ul>
  <li>MyApp.iOS - application for iOS</li>
  <li>MyApp.Android - application for Android</li>
  <li>MyApp.UITests.iOS - where is only reference to iOS project and shared library</li>
  <li>MyApp.UITests.Android - where is only reference to Android project and shared library</li>
  <li>MyApp.UITests.SharedLibrary - with all test cases</li>
  </ul>
  
  <p>When I am building this in MSBuild I have many errors with:</p>
  
  <blockquote>
    <p>/Users/vstsagent/MyApp.UITests.SharedLibrary/...: error CS0246: The
    type or namespace name `Xamarin' could not be found.</p>
  </blockquote>
  
  <p>It looks like problem is compilation of my SharedLibrary project.</p>