Make LOCK_PRINT & PROCLOCK_PRINT expand to ((void) 0) when not in use.

This avoids warnings from more-anal-than-average compilers, and might
prevent hidden syntax problems in the future.

Andres Freund

src/backend/storage/lmgr/lock.c

@@ -331,8 +331,8 @@ PROCLOCK_PRINT(const char *where, const PROCLOCK *proclockP)
 }
 #else							/* not LOCK_DEBUG */
 
-#define LOCK_PRINT(where, lock, type)
-#define PROCLOCK_PRINT(where, proclockP)
+#define LOCK_PRINT(where, lock, type)  ((void) 0)
+#define PROCLOCK_PRINT(where, proclockP)  ((void) 0)
 #endif   /* not LOCK_DEBUG */