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/lwpint.h

@@ -89,6 +89,7 @@ void lwpReady(struct lwpProc *);
 void lwpReschedule(void);
 void lwpEntryPoint(void);
 void lwpInitSelect(struct lwpProc *);
+void lwpWakeupSleep(void);
 void lwpSelect(void *);
 void lwpInitSigWait(sigset_t *);
 void lwpSigWakeup(void);