title: Adding C file causes pch error
body: <p>I have an <code>XCode</code> project with <code>objective-C</code> files.  If I add a new (empty) <code>C file</code> and try to build, I get a large number of errors right away while building a precompiled header, in ProcessPCH step.  The errors are "fatal error: Could not build module 'Foundation'", and things in <code>Foundation.h</code> not being found. Remove the C file and it builds again.  What is going on, and how to fix it?</p>
  
  <p><strong>(XCode 5.0, OSX 10.8.4)</strong></p>
  
  <p><em>EDIT</em> I have tried Clean and Clean build folder, no effect.</p>
  
  <p><em>EDIT</em> Setting <code>Precompile prefix header = No</code> results in a bunch of syntax errors instead, in stuff like <code>NSObject.h</code> (and other Foundation framework header).</p>
  
  <p><em>EDIT</em> User Cy-4AH figured it out: there needs to be <code>#ifdef __OBJC__</code> around the <em>whole</em> pch file.</p>