Append system paths to $PATH.

def append_system_paths(self):
        """Append system paths to $PATH."""
        from rez.shells import Shell, create_shell
        sh = self.interpreter if isinstance(self.interpreter, Shell) \
            else create_shell()

        paths = sh.get_syspaths()
        paths_str = os.pathsep.join(paths)
        self.env.PATH.append(paths_str)