Attempt to fix compiler warning on old compiler

A couple more like b449afb582, per
complaints from lapwing.

contrib/pg_prewarm/autoprewarm.c

@@ -814,11 +814,12 @@ apw_detach_shmem(int code, Datum arg)
 static void
 apw_start_leader_worker(void)
 {
-	BackgroundWorker worker = {0};
+	BackgroundWorker worker;
 	BackgroundWorkerHandle *handle;
 	BgwHandleStatus status;
 	pid_t		pid;
 
+	MemSet(&worker, 0, sizeof(BackgroundWorker));
 	worker.bgw_flags = BGWORKER_SHMEM_ACCESS;
 	worker.bgw_start_time = BgWorkerStart_ConsistentState;
 	strcpy(worker.bgw_library_name, "pg_prewarm");
@@ -855,9 +856,10 @@ apw_start_leader_worker(void)
 static void
 apw_start_database_worker(void)
 {
-	BackgroundWorker worker = {0};
+	BackgroundWorker worker;
 	BackgroundWorkerHandle *handle;
 
+	MemSet(&worker, 0, sizeof(BackgroundWorker));
 	worker.bgw_flags =
 		BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION;
 	worker.bgw_start_time = BgWorkerStart_ConsistentState;

contrib/postgres_fdw/postgres_fdw.c

@@ -3307,7 +3307,7 @@ estimate_path_cost_size(PlannerInfo *root,
 		{
 			RelOptInfo *outerrel = fpinfo->outerrel;
 			PgFdwRelationInfo *ofpinfo;
-			AggClauseCosts aggcosts = {0};
+			AggClauseCosts aggcosts;
 			double		input_rows;
 			int			numGroupCols;
 			double		numGroups = 1;
@@ -3331,6 +3331,7 @@ estimate_path_cost_size(PlannerInfo *root,
 			input_rows = ofpinfo->rows;
 
 			/* Collect statistics about aggregates for estimating costs. */
+			MemSet(&aggcosts, 0, sizeof(AggClauseCosts));
 			if (root->parse->hasAggs)
 			{
 				get_agg_clause_costs(root, AGGSPLIT_SIMPLE, &aggcosts);