Too dangerous:
m3cc/src/m3makefile
if stale(build_dir & "/clean_marker.txt", "../src/clean_marker.txt") or defined ("FORCE")
  m3cc_Run(["rm -rf " & build_dir & "/*"])
  cp_if("../src/clean_marker.txt", build_dir & "/clean_marker.txt") 
end
?
If build_dir has a space..?
 - Jay