title: How do you enable "#ifndef/#endif" blocks in makefile builds?
body: <p>I'm trying to enable debugging options in MuPDF. For some reason they have used <code>#ifndef NDEBUG</code> and <code>#endif</code> greying out code I want to use. I searched throughout the library but couldn't find any traces of NDEBUG defined anywhere. I've managed to work around this by adding <code>#undef NDEBUG</code> in a header, but I would like to know if there is a more non-intrusive method to do so.</p>
  
  <p>SO, can you enable "#ifndef/#endif" blocks from the makefile?</p>
  
  <p>Also, why would you use <code>#ifndef</code> to grey out code? Isn't it supposed to be <code>#ifdef NDEBUG</code>?</p>