title: How to add extra clean targets while using SCons
body: <p>I have a hierarchical build that use SConscript to declare build target recursively; so I don't know the targets beforehand. Each build will produce some extra files like *.err *.out that are not in targets. When I run scons -c, those files will be left uncleaned. </p>
  
  <p>Is there a way to clean those file when I run scons -c?</p>