Fix unportable printf format introduced in commit 9290ad198.

"%ld" is not an acceptable format spec for int64 variables, though
it accidentally works on most non-Windows 64-bit platforms.  Follow
the lead of commit 6a1cd8b92, and use "%lld" with an explicit cast
to long long.  Per buildfarm.

src/backend/replication/walsender.c

@@ -3644,8 +3644,11 @@ UpdateSpillStats(LogicalDecodingContext *ctx)
 	MyWalSnd->spillCount = rb->spillCount;
 	MyWalSnd->spillBytes = rb->spillBytes;
 
-	elog(DEBUG2, "UpdateSpillStats: updating stats %p %ld %ld %ld",
-		 rb, rb->spillTxns, rb->spillCount, rb->spillBytes);
+	elog(DEBUG2, "UpdateSpillStats: updating stats %p %lld %lld %lld",
+		 rb,
+		 (long long) rb->spillTxns,
+		 (long long) rb->spillCount,
+		 (long long) rb->spillBytes);
 
 	SpinLockRelease(&MyWalSnd->mutex);
 }