On both i486 and ia64 Linux the runtime code traps SIGCHLD and handles it as
follows:

  /* from os_linux_i486.cpp; ia64 code is identical */
  if (sig == SIGCHLD) {
    // cleanup zombie pid for child thread
    ::waitpid(-1, 0, WNOHANG);
    return 1;
  }

This test, and the corresponding setup of the signal handler to catch SIGCHLD,
serve no purpose and should be removed. (See 4763362 for details.)