title: Reference to 'X' is ambiguous
body: <p>After several changes to my project I suddenly get this build error:</p>
  
  <blockquote>
    <p>Reference to 'kCGImageAlphaPremultipliedLast' is ambiguous</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/2jyJA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2jyJA.png" alt="Reference is ambiguous error screenshot"></a></p>
  
  <p>and when when taking a look at the error it shows me that it is referenced 4 times:</p>
  
  <p><a href="https://i.stack.imgur.com/RiO6n.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RiO6n.png" alt="Xcode error screenshot"></a></p>
  
  <p>Can someone please tell me how this can happen and how can I figure out what is causing this? I am not importing anything from CoreGraphics explicitly and my Prefix file only imports ´Foundation.h´ and some self made macros. I am however importing several headers containing pure C code but they are all encapsulated in something like this:</p>
  
  <pre><code>#ifndef __MYCCODE_H
  #define __MYCCODE_H
  // imports here
  // c code here
  #endif
  </code></pre>
  
  <p>This happens in Xcode 5 using LLVM 5.1</p>
  
  <p>Edit: this seems to be a different problem with this project. after commenting this line of code I get another error:</p>
  
  <blockquote>
    <p>Malformed or corrupted AST file: 'Unable to load module "/Users/xxx/Library/Developer/Xcode/DerivedData/ModuleCache/1NHZ5MC2OSMJV/CoreImage.pcm": module file out of date'</p>
  </blockquote>
  
  <p>Removing the module and adding it again did not help. Deleting the derived data also didn't help. This error also appears when going back to a working commit.</p>