Fix compiler warnings due to new checks in PostgreSQL 16

See the commit 0fe954c28584169938e5c0738cfaa9930ce77577 (Add
-Wshadow=compatible-local to the standard compilation flags) in PostgreSQL 16.

Author: Marina Polyakova

src/partition_creation.c

@@ -2027,11 +2027,9 @@ build_partitioning_expression(Oid parent_relid,
 	/* We need expression type for hash functions */
 	if (expr_type)
 	{
-		Node	*expr;
-		expr = cook_partitioning_expression(parent_relid, expr_cstr, NULL);
-
 		/* Finally return expression type */
-		*expr_type = exprType(expr);
+		*expr_type = exprType(
+			cook_partitioning_expression(parent_relid, expr_cstr, NULL));
 	}
 
 	if (columns)

src/relation_info.c

@@ -71,34 +71,34 @@ int				prel_resowner_line = 0;
 
 #define LeakTrackerAdd(prel) \
 	do { \
-		MemoryContext old_mcxt = MemoryContextSwitchTo((prel)->mcxt); \
+		MemoryContext leak_tracker_add_old_mcxt = MemoryContextSwitchTo((prel)->mcxt); \
 		(prel)->owners = \
 				list_append_unique( \
 						(prel)->owners, \
 						list_make2(makeString((char *) prel_resowner_function), \
 								   makeInteger(prel_resowner_line))); \
-		MemoryContextSwitchTo(old_mcxt); \
+		MemoryContextSwitchTo(leak_tracker_add_old_mcxt); \
 		\
 		(prel)->access_total++; \
 	} while (0)
 
 #define LeakTrackerPrint(prel) \
 	do { \
-		ListCell *lc; \
-		foreach (lc, (prel)->owners) \
+		ListCell *leak_tracker_print_lc; \
+		foreach (leak_tracker_print_lc, (prel)->owners) \
 		{ \
-			char   *fun = strVal(linitial(lfirst(lc))); \
-			int		line = intVal(lsecond(lfirst(lc))); \
+			char   *fun = strVal(linitial(lfirst(leak_tracker_print_lc))); \
+			int		line = intVal(lsecond(lfirst(leak_tracker_print_lc))); \
 			elog(WARNING, "PartRelationInfo referenced in %s:%d", fun, line); \
 		} \
 	} while (0)
 
 #define LeakTrackerFree(prel) \
 	do { \
-		ListCell *lc; \
-		foreach (lc, (prel)->owners) \
+		ListCell *leak_tracker_free_lc; \
+		foreach (leak_tracker_free_lc, (prel)->owners) \
 		{ \
-			list_free_deep(lfirst(lc)); \
+			list_free_deep(lfirst(leak_tracker_free_lc)); \
 		} \
 		list_free((prel)->owners); \
 		(prel)->owners = NIL; \

src/runtime_merge_append.c

@@ -374,7 +374,8 @@ fetch_next_tuple(CustomScanState *node)
 		for (i = 0; i < scan_state->rstate.ncur_plans; i++)
 		{
 			ChildScanCommon		child = scan_state->rstate.cur_plans[i];
-			PlanState		   *ps = child->content.plan_state;
+
+			ps = child->content.plan_state;
 
 			Assert(child->content_type == CHILD_PLAN_STATE);
 
@@ -721,10 +722,11 @@ prepare_sort_from_pathkeys(PlannerInfo *root, Plan *lefttree, List *pathkeys,
 
 			foreach(j, ec->ec_members)
 			{
-				EquivalenceMember *em = (EquivalenceMember *) lfirst(j);
 				List	   *exprvars;
 				ListCell   *k;
 
+				em = (EquivalenceMember *) lfirst(j);
+
 				/*
 				 * We shouldn't be trying to sort by an equivalence class that
 				 * contains a constant, so no need to consider such cases any