title: Xcode 7 not using compiled header for error warnings
body: <p>I upgraded to Xcode 7 yesterday and I'm getting a bunch of errors from Xcode. The program compiles / runs fine, but when programming it says things like <code>No known class method for selector...</code>, <code>Use of undeclared identifier</code>, <code>No visible @interface for...</code>, or <code>Receiver type '...' for instance message is a forward declaration</code>.</p>
  
  <p>All of these errors, I assume, are coming up because it isn't using my precompiled header (<code>*.pch</code>) which includes the files needed for it to know about those classes.</p>
  
  <p>How do I tell Xcode to look at the precompiled header?</p>
  
  <p>I'm only using Objective-C.</p>