Make SyncRepWakeQueue to a static function

It is only used in src/backend/replication/syncrep.c.

Back-patch to all supported branches except 9.1 which declares the
function as static.

src/backend/replication/syncrep.c

@@ -69,6 +69,7 @@ static int	SyncRepWaitMode = SYNC_REP_NO_WAIT;
 
 static void SyncRepQueueInsert(int mode);
 static void SyncRepCancelWait(void);
+static int	SyncRepWakeQueue(bool all, int mode);
 
 static int	SyncRepGetStandbyPriority(void);
 
@@ -529,7 +530,7 @@ SyncRepGetStandbyPriority(void)
  *
  * Must hold SyncRepLock.
  */
-int
+static int
 SyncRepWakeQueue(bool all, int mode)
 {
 	volatile WalSndCtlData *walsndctl = WalSndCtl;

src/include/replication/syncrep.h

@@ -47,9 +47,6 @@ extern void SyncRepReleaseWaiters(void);
 /* called by checkpointer */
 extern void SyncRepUpdateSyncStandbysDefined(void);
 
-/* called by various procs */
-extern int	SyncRepWakeQueue(bool all, int mode);
-
 extern bool check_synchronous_standby_names(char **newval, void **extra, GucSource source);
 extern void assign_synchronous_commit(int newval, void *extra);