title: Xcode 9 undefined symbols for architecture x86_64
body: <p>after switching to Xcode 9 I am getting errors, it looks like this.</p>
  
  <p><a href="https://i.stack.imgur.com/rpq6T.png" rel="noreferrer"><img src="https://i.stack.imgur.com/rpq6T.png" alt="enter image description here"></a></p>
  
  <p>I blanked the project and classes names, but there is a list of classess ending with .o suffix. In Xcode 8.3.2 everything works. I  got 2 projects, one is library that is building without problems. Another project is test app, that is pointing to the library by :path directive in Podfile. In both projects build settings -> architectures is set to standard arichitectures, build active architectures only is set to DEBUG: Yes, RELEASE: No. Have you come across this problem? Thanks upfront for the   help.</p>