Revert "Disable the timer signal while blocked in select() (#5991)"

This reverts commit dd24d6bc.

This attempt to fix the problem was misguided: the program might be
stuck in a foreign call rather than awaitEvent(), and then the timer
signal will never get disabled.  The only way to turn off the timer
signal in this case is in the timer interrupt handler itself.

MERGED from commit 673b6f50

rts/posix/Select.c

@@ -212,19 +212,10 @@ awaitEvent(rtsBool wait)
           ptv = NULL;
       }
 
-      while (1) { // repeat the select on EINTR
-
-          // Disable the timer signal while blocked in
-          // select(), to conserve power. (#1623, #5991)
-          if (wait) stopTimer();
-
-          numFound = select(maxfd+1, &rfd, &wfd, NULL, ptv);
-
-          if (wait) startTimer();
-
-          if (numFound >= 0) break;
-
-          if (errno != EINTR) {
+      /* Check for any interesting events */
+      
+      while ((numFound = select(maxfd+1, &rfd, &wfd, NULL, ptv)) < 0) {
+	  if (errno != EINTR) {
 	    /* Handle bad file descriptors by unblocking all the
 	       waiting threads. Why? Because a thread might have been
 	       a bit naughty and closed a file descriptor while another