title: What #defines are set up by Xcode when compiling for iPhone
body: <p>I'm writing some semi-portable code and want to be able to detect when I'm compiling for iPhone. So I want something like <code>#ifdef IPHONE_SDK...</code>. </p>
  
  <p>Presumably Xcode defines something, but I can't see anything under project properties, and Google isn't much help.</p>