title: Mixing swift and objective-c in WatchKitExtension
body: <p>I am getting following warnings and errors while in my <code>WatchKit</code> extension:</p>
  
  <pre><code>Warning: no rule to process file 'App-Bridging-Header.h' of type sourcecode.c.h for architecture x86_64
  
  /Users/janusz/Desktop/Repositories/RunnerAppWatch/Source/WormholeMessanger.swift:12:20: Use of unresolved identifier 'MMWormhole'
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/05mUU.png" alt="Bridge Header"></p>
  
  <p>It's also listed in Compiled Sources section. </p>
  
  <p>Everything works fine when I delete the <code>WatchKit</code> Extension, but once I add it back I am getting errors again. 
  So the question is: how to make bridging header work with the <code>WatchKit</code> Extension? 
  Thanks!</p>