Run the doxygen make command in the designated folder.

def run_doxygen(folder):
  """Run the doxygen make command in the designated folder."""
  try:
    retcode = subprocess.call("cd %s; make doxygen" % folder, shell=True)
    if retcode < 0:
      sys.stderr.write("doxygen terminated by signal %s" % (-retcode))
  except OSError as e:
    sys.stderr.write("doxygen execution failed: %s" % e)