Merge branch 'rb/compat-poll-fix' into maint

Backports a moral equivalent of 2015 fix to the poll emulation from
the upstream gnulib to fix occasional breakages on HPE NonStop.

* rb/compat-poll-fix:
  poll.c: always set revents, even if to zero

compat/poll/poll.c

@@ -438,6 +438,10 @@ poll (struct pollfd *pfd, nfds_t nfd, int timeout)
 	    pfd[i].revents = happened;
 	    rc++;
 	  }
+	else
+	  {
+	    pfd[i].revents = 0;
+	  }
       }
 
   return rc;