Hi,
I tested the hideif.el patch from Joe. It works in some cases but does not seem to work with a series of #elif's like this case:
#if 0
   function1();
#elif 1
   function2(); // should not be hidden but is hidden
#elif 0
   function3();
#elif 0
   function4();
#endif

I do not have a fix (at least not right now).

Thanks,
Tony