title: Good way to document #undef in doxygen
body: <p>I currently have a couple of #define in c files that turn off some functionality to hardware for testing. However, I want to document them with doxygen when they are undefined as well.</p>
  
  <p>For example:</p>
  
  <p>This works fine:</p>
  
  <pre><code>/// \def SIMULATE_SOME_HW_INTERFACE
  /// Define this when you want to simulate HW interface.
  #define SIMULATE_SOME_HW_INTERFACE
  </code></pre>
  
  <p>When you change the #define to #undef, you get a warning in doxygen, and it doesn't show up in the doxygen generated output. I want to document this #define wether it's defined or undefined.</p>
  
  <p>How can I force doxygen to document a #undef???</p>