code: def on_windows ():
      
      if bjam.variable("NT"):
          return True
  
      elif bjam.variable("UNIX"):
  
          uname = bjam.variable("JAMUNAME")
          if uname and uname[0].startswith("CYGWIN"):
              return True
  
      return False
docs: Returns true if running on windows, whether in cygwin or not.