title: Tool for compiling automatically all ifdef / ifndef directives
body: <p>My <strong>C</strong> project uses preprocessor directives to activate / deactivate some features. It's not unusual to find some of the less common configurations do not compile anymore due to a change made a few days ago within an <code>#ifdef</code>.</p>
  
  <p>We use a script to compile the most common configurations, but I'm looking for a tool to ensure everything is compiled (testing is not a problem in our case, we just want to detect ASAP nothing stops compiling). Usually ifdefs / ifndefs are independent, so normally each module have to be compiled just twice (all symbols defined, all undefined). But sometimes the ifdefs are nested, so those modules have to be compiled more times.</p>
  
  <p>Do you know of any tool to search all ifdef / ifndef (also nested ones) and gives how many times a module have to be compiled (with the set of preprocessor symbols to be defined in each one) to ensure every single source line of code is analyzed by the compiler?</p>