Merge "Wait for children to exit in makeparallel"

  static pid_t pid;

  // Set up signal handlers to forward SIGTERM to child

  // Assume that all other signals are sent to the entire process group

  // Set up signal handlers to forward SIGTERM to child.

  // Assume that all other signals are sent to the entire process group,

  // and that we'll wait for our child to exit instead of handling them.

  struct sigaction action = {};

  action.sa_flags = SA_SIGINFO | SA_RESTART,

  action.sa_sigaction = [](int signal, siginfo_t*, void*) {

    if (pid > 0) {

  action.sa_flags = SA_RESTART;

  action.sa_handler = [](int signal) {

    if (signal == SIGTERM && pid > 0) {

      kill(pid, signal);

    }

  };

  int ret = 0;

  if (!ret) ret = sigaction(SIGHUP, &action, NULL);

  if (!ret) ret = sigaction(SIGINT, &action, NULL);

  if (!ret) ret = sigaction(SIGQUIT, &action, NULL);

  if (!ret) ret = sigaction(SIGTERM, &action, NULL);

  if (!ret) ret = sigaction(SIGALRM, &action, NULL);

  if (ret < 0) {

    error(errno, errno, "sigaction failed");

  }