Rename shadowed local variables

In a similar effort to f01592f91, here we mostly rename shadowed local
variables to remove the warnings produced when compiling with
-Wshadow=compatible-local.

This fixes 63 warnings and leaves just 5.

Author: Justin Pryzby, David Rowley
Reviewed-by: Justin Pryzby
Discussion https://postgr.es/m/20220817145434.GC26426%40telsasoft.com

src/backend/replication/logical/reorderbuffer.c

@@ -2320,17 +2320,17 @@ ReorderBufferProcessTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
 						for (i = 0; i < nrelids; i++)
 						{
 							Oid			relid = change->data.truncate.relids[i];
-							Relation	relation;
+							Relation	rel;
 
-							relation = RelationIdGetRelation(relid);
+							rel = RelationIdGetRelation(relid);
 
-							if (!RelationIsValid(relation))
+							if (!RelationIsValid(rel))
 								elog(ERROR, "could not open relation with OID %u", relid);
 
-							if (!RelationIsLogicallyLogged(relation))
+							if (!RelationIsLogicallyLogged(rel))
 								continue;
 
-							relations[nrelations++] = relation;
+							relations[nrelations++] = rel;
 						}
 
 						/* Apply the truncate. */

src/backend/replication/walreceiver.c

@@ -180,7 +180,7 @@ WalReceiverMain(void)
 	bool		first_stream;
 	WalRcvData *walrcv = WalRcv;
 	TimestampTz last_recv_timestamp;
-	TimestampTz now;
+	TimestampTz starttime;
 	bool		ping_sent;
 	char	   *err;
 	char	   *sender_host = NULL;
@@ -192,7 +192,7 @@ WalReceiverMain(void)
 	 */
 	Assert(walrcv != NULL);
 
-	now = GetCurrentTimestamp();
+	starttime = GetCurrentTimestamp();
 
 	/*
 	 * Mark walreceiver as running in shared memory.
@@ -248,7 +248,7 @@ WalReceiverMain(void)
 
 	/* Initialise to a sanish value */
 	walrcv->lastMsgSendTime =
-		walrcv->lastMsgReceiptTime = walrcv->latestWalEndTime = now;
+		walrcv->lastMsgReceiptTime = walrcv->latestWalEndTime = starttime;
 
 	/* Report the latch to use to awaken this process */
 	walrcv->latch = &MyProc->procLatch;