title: Can't launch tests with XCTest
body: <p>Everything worked fine, but on some build I've got this (when trying to launch tests):</p>
  
  <blockquote>
    <p>The test bundle at "path to xctest" could not be loaded because it is
    built for a different architecture than the currently-running test rig
    (which is running as x86_64)</p>
  </blockquote>
  
  <p>What am I doing wrong? I've tried to rebuild, clean, relaunch Xcode, reboot OS X...</p>