title: Xcode build fails with "fatal error: malformed or corrupted AST file" Crashlytics.h
body: <p>I recently enabled modules in my Xcode project build settings ("Enable Modules (C and Objective-C)") and now I frequently get the below build error. It works the next time I build (without any changes) but it is annoying because it happens very often (several times an hour).</p>
  
  <blockquote>
    <p>fatal error: malformed or corrupted AST file: 'could not find file
    '/Users/mpv/dev/project/Crashlytics.framework/Headers/Crashlytics.h'
    referenced by AST file' note: after modifying system headers, please
    delete the module cache at
    '/Users/mpv/Library/Developer/Xcode/DerivedData/ModuleCache/M5WJ0FYE7N06'</p>
  </blockquote>
  
  <p>Crashlytics recommended removing Crashlytics.h from the precompiled header file (.pch) and importing directly in each source file that needs it. This greatly reduces the problem but I still occasionally get a Crashlytics.h file not found error when building.</p>
  
  <pre><code>fatal error: 'Crashlytics/Crashlytics.h' file not found
  #import &lt;Crashlytics/Crashlytics.h&gt;
  </code></pre>