Not quite all codes are silent. ICC 700-2008 National Green Building Standard Section 802.2 gives 8 points for each composting or waterless toilet and urinal installed up to a max of 24 points and an additional 8 points if all installed toilets and urinals are waterless.
Cleavus Multrum is a major manufacturer
Clivus Multrum, Inc.: Manufacturer of Composting Toilets and Greywater Systems since 1973
I have used them in backcountry sites and scout camps they have some limitations and are high maintenance--have to add the much or leaves each use and if sanitizing cleaners or bleach is dumped in the toilet you end up with a real stinky mess because it kills the bugs that are doing the composting--big problem at the girl scout camp by well meaning leaders. Some are solar powered for the exuast fan others use a black painted chimney to draw the oders out of the composting chamber via natural ventilation.