title: FBSDKLoginManager: undefined symbols for architecture x86_64 + linker command failed with exit code 1
body: <p>I just upgraded Facebook iOS SDK to v.4.0.1 and I got these errors:</p>
  
  <pre><code>Undefined symbols for architecture x86_64:
    "_OBJC_CLASS_$_FBSDKLoginManager", referenced from:
        objc-class-ref in Controller1.o
        objc-class-ref in AppDelegate.o
        objc-class-ref in Controller2.o
  ld: symbol(s) not found for architecture x86_64
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>I already tried to change linkers: with <em>-all_load</em> I get the same error, while with <em>-force_load</em> it becomes "ld: file not found: -fobjc-arc". Any solutions?</p>