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

The threaded RTS had a fix for this a long time ago (#1623) but this
patch applies a similar fix to the non-threaded RTS.

rts/posix/Select.c

@@ -196,10 +196,19 @@ awaitEvent(rtsBool wait)
           ptv = NULL;
       }
 
-      /* Check for any interesting events */
-      
-      while ((numFound = select(maxfd+1, &rfd, &wfd, NULL, ptv)) < 0) {
-	  if (errno != EINTR) {
+      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) {
 	    /* 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