Handle some OS/390-isms dealing with pthreads:

. the types of the parameters to pthread_attr_setdetachstate()
  and pthread_detach()
. the fact that sigprocmask() must be use to set a thread's
  signal mask


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85230 13f79535-47bb-0310-9956-ffa450edef68