title: Xcode 6.1 Missing required architecture X86_64 in file
body: <p>In Xcode 6.1 , I am getting error for iPhone 6, iPhone 5s(iOS 7.1) which says </p>
  
  <pre><code>    Undefined symbols for architecture x86_64:
        "_OBJC_CLASS_$_ClientAuthenticator", referenced from:
        objc-class-ref in AppDelegate.o
  ld: symbol(s) not found for architecture x86_64
  linker command failed with exit code 1
  </code></pre>
  
  <p>This is what I have for architecture settings perspective </p>
  
  <pre><code>  Architectures : Standard Architectures(armv7, arm64) - $(ARCHES_STANDARD)
    Base SDK : Latest iOS(8.1) 
    Valid Architectures: arm64, armv7, armv7s
  
    IOS Deployment Target: iOS 6.0
  </code></pre>
  
  <p>Recently I updated my OS to Yosemite and Xcode from 6.0 to 6.1. I have searched on Stack Overflow for this question which refer to Xcode 5.1 and tried all the given solutions, but nothing has worked. </p>
  
  <p><strong>Update</strong> - I tried the changes as suggested in the answer, but I still keep getting the error which says "<strong>Missing required architecture X86_64</strong>" . On further investigation I found that the file ClientAuthenticator.o which is from my library is not getting built for X86_64 architecture and probably that is the issue? I am looking how it can be built for x86_64. </p>
  
  <p>My new question is <strong>what is the difference between arm64 and x86_64</strong>? More of it seems like the difference between just the architecture manufacturer, but basic 64-bit architecture remains same.</p>