title: How to define a preprocessor symbol in Xcode
body: <p>Is it possible to set a symbol for conditional compilation by setting up properties in an Xcode project?</p>
  
  <p>My aim is to to create a symbol that is available to all files, without having to use import/include, so that a set of common classes can have a special behavior in some projects. Like the following, but with my own symbols.</p>
  
  <pre><code>#if TARGET_IPHONE_SIMULATOR
      ...
  #endif
  </code></pre>