sync: Avoid ridiculously long timeouts

On OpenBSD, passing a timeout longer than 100000000 seconds to select(2) will
make it fail with EINVAL.  As this is original 4.4BSD behaviour it is not
inconceivable that other systems suffer from the same problem.  And Linux,
though not suffering from any 4.4BSD heritage, briefly did something similar:

<https://lkml.org/lkml/2012/8/31/263>

So avoid calling AdjustWaitForDelay() instead of setting the timeout to
(effectively) ULONG_MAX milliseconds.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Matthieu Herrb <matthieu@herrb.eu>
(cherry picked from commit ddeca92749)

Xext/sync.c

@@ -2731,27 +2731,24 @@ IdleTimeBlockHandler(pointer pCounter, struct timeval **wt, pointer LastSelectMa
          * If we've been idle more than it, and someone wants to know about
          * that level-triggered, schedule an immediate wakeup.
          */
-        unsigned long timeout = -1;
 
         if (XSyncValueLessThan(idle, *greater)) {
             XSyncValue value;
             Bool overflow;
 
             XSyncValueSubtract(&value, *greater, idle, &overflow);
-            timeout = min(timeout, XSyncValueLow32(value));
+            AdjustWaitForDelay(wt, XSyncValueLow32(value));
         }
         else {
             for (list = counter->sync.pTriglist; list;
                  list = list->next) {
                 trig = list->pTrigger;
                 if (trig->CheckTrigger(trig, old_idle)) {
-                    timeout = min(timeout, 0);
+                    AdjustWaitForDelay(wt, 0);
                     break;
                 }
             }
         }
-
-        AdjustWaitForDelay(wt, timeout);
     }
 
     counter->value = old_idle;  /* pop */