LWP failed to wake up threads sleeping in empth_sleep() while other

threads were runnable.  This let players with a sufficiently fast
connection starve out system threads, including the update.  Fix:
[EMPTH_LWP] (lwpWakeupSleep): External linkage.
[EMPTH_LWP] (lwpReschedule): Call it.

src/lib/lwp/lwp.c

@@ -76,6 +76,7 @@ lwpReschedule(void)
     }
 
     lwpSigWakeup();
+    lwpWakeupSleep();
 
     /* destroy dead threads */
     lwpStatus(LwpCurrent, "Cleaning dead queue");