title: Dupplicate symbols errors when adding OpenKit
body: <p>I'm trying to add a leaderboard to my game by using <a href="http://openkit.io/documentation/" rel="nofollow">OpenKit</a> Framework. Following their documentation, I've added all the neccessay libs + framwork but the following errors occured :</p>
  
  <pre><code>duplicate symbol _OBJC_IVAR_$_AFOAuth1Client._applicationLaunchNotificationObserver in:
    /Users/Sa7bi/Library/Developer/Xcode/DerivedData/helloworld-erlcedkitaorqobgauzlzyvacnfi/Build/Intermediates/helloworld.build/Debug-iphoneos/helloworld.build/Objects-normal/armv7s/AFOAuth1Client.o
    /Users/Sa7bi/Dropbox/Aliens Wings/HelloWorld/OpenKitSDK/libOpenKit.a(AFOAuth1Client.o)
  duplicate symbol _OBJC_IVAR_$_AFOAuth1Client._key in:
    /Users/Sa7bi/Library/Developer/Xcode/DerivedData/helloworld-erlcedkitaorqobgauzlzyvacnfi/Build/Intermediates/helloworld.build/Debug-iphoneos/helloworld.build/Objects-normal/armv7s/AFOAuth1Client.o
    /Users/Sa7bi/Dropbox/Aliens Wings/HelloWorld/OpenKitSDK/libOpenKit.a(AFOAuth1Client.o)
  duplicate symbol _OBJC_IVAR_$_AFOAuth1Client._secret in:
    /Users/Sa7bi/Library/Developer/Xcode/DerivedData/helloworld-erlcedkitaorqobgauzlzyvacnfi/Build/Intermediates/helloworld.build/Debug-iphoneos/helloworld.build/Objects-normal/armv7s/AFOAuth1Client.o
    /Users/Sa7bi/Dropbox/Aliens Wings/HelloWorld/OpenKitSDK/libOpenKit.a(AFOAuth1Client.o)
  duplicate symbol _OBJC_IVAR_$_AFOAuth1Client._signatureMethod in:
    /Users/Sa7bi/Library/Developer/Xcode/DerivedData/helloworld-erlcedkitaorqobgauzlzyvacnfi/Build/Intermediates/helloworld.build/Debug-iphoneos/helloworld.build/Objects-normal/armv7s/AFOAuth1Client.o
    /Users/Sa7bi/Dropbox/Aliens Wings/HelloWorld/OpenKitSDK/libOpenKit.a(AFOAuth1Client.o)
  duplicate symbol _OBJC_IVAR_$_AFOAuth1Client._realm in:
    /Users/Sa7bi/Library/Developer/Xcode/DerivedData/helloworld-erlcedkitaorqobgauzlzyvacnfi/Build/Intermediates/helloworld.build/Debug-iphoneos/helloworld.build/Objects-normal/armv7s/AFOAuth1Client.o
    /Users/Sa7bi/Dropbox/Aliens Wings/HelloWorld/OpenKitSDK/libOpenKit.a(AFOAuth1Client.o)
  ....
  ld: 19 duplicate symbols for architecture armv7s
  </code></pre>
  
  <p>While searching on this website, some users suggested the following:</p>
  
  <ul>
  <li>Compilation of the same file more than once ==> checked my [Build Phases | Compile Sources] nothing</li>
  <li>Importing ".m" files instead of ".h" ==> checked all my imports, nothing</li>
  </ul>
  
  <p>I really have no idea what is causing this.
  <strong>Update</strong>: I have forget to mention that Google Ads SDK is included in my projet. When I delete the "-ObjC" linker flag, OpenKit works fine but Google doesn't.</p>