title: Xcode: Setting GCC_PREPROCESSOR_DEFINITIONS for different build configurations?
body: <p>I want to set <code>GCC_PREPROCESSOR_DEFINITIONS</code> for each of my four build configurations (Debug, Release, Ad Hoc, and Distribution.) I'd like to have a different setting for each. </p>
  
  <p>The screen I'm looking at is the Target Info window's "Build" tab. When I set the Configuration pop-up to "Debug" I can see my <code>GCC_PREPROCESSOR_DEFINITIONS</code> setting there. When I switch to "Release," or any of the other configurations, it's no longer visible. Yet when I try to add it to those configurations, it says <code>GCC_PREPROCESSOR_DEFINITIONS</code> already exists, and that I can't add it again.</p>
  
  <p>As I said, I want to have a different setting for my various builds. How can I accomplish this?</p>
  
  <p>Thanks very much.</p>