Fix a build issue with v11.

Upstream commit 8237f27b504ff1d1e2da7ae4c81a7f72ea0e0e3e removed
get_relid_attribute_name and added missing_ok get_attname so it
can serve the purpose of get_relid_attribute_name.  This commit
replace get_relid_attribute_name() to get_attname().

mongo_fdw.c

@@ -956,7 +956,11 @@ MongoExecForeignUpdate(EState *estate,
 	/* Get the id that was passed up as a resjunk column */
 	datum = ExecGetJunkAttribute(planSlot, 1, &isNull);
 
+#if PG_VERSION_NUM < 110000
 	columnName = get_relid_attribute_name(foreignTableId, 1);
+#else
+	columnName = get_attname(foreignTableId, 1, false);
+#endif
 
 	typoid = get_atttype(foreignTableId, 1);
 
@@ -1061,7 +1065,11 @@ MongoExecForeignDelete(EState *estate,
 	/* Get the id that was passed up as a resjunk column */
 	datum = ExecGetJunkAttribute(planSlot, 1, &isNull);
 
+#if PG_VERSION_NUM < 110000
 	columnName = get_relid_attribute_name(foreignTableId, 1);
+#else
+	columnName = get_attname(foreignTableId, 1, false);
+#endif
 
 	typoid = get_atttype(foreignTableId, 1);
 
@@ -1177,7 +1185,11 @@ ColumnMappingHash(Oid foreignTableId, List *columnList)
 		bool handleFound = false;
 		void *hashKey = NULL;
 
+#if PG_VERSION_NUM < 110000
 		columnName = get_relid_attribute_name(foreignTableId, columnId);
+#else
+		columnName = get_attname(foreignTableId, columnId, false);
+#endif
 		hashKey = (void *) columnName;
 
 		columnMapping = (ColumnMapping *) hash_search(columnMappingHash, hashKey,

mongo_query.c

@@ -210,7 +210,11 @@ QueryDocument(Oid relationId, List *opExpressionList, ForeignScanState *scanStat
 		paramNode = (Param *) FindArgumentOfType(argumentList, T_Param);
 
 		columnId = column->varattno;
+#if PG_VERSION_NUM < 110000
 		columnName = get_relid_attribute_name(relationId, columnId);
+#else
+		columnName = get_attname(relationId, columnId, false);
+#endif
 
 		if (constant != NULL)
 			AppendConstantValue(queryDocument, columnName, constant);
@@ -238,7 +242,11 @@ QueryDocument(Oid relationId, List *opExpressionList, ForeignScanState *scanStat
 		BSON r;
 
 		columnId = column->varattno;
+#if PG_VERSION_NUM < 110000
 		columnName = get_relid_attribute_name(relationId, columnId);
+#else
+		columnName = get_attname(relationId, columnId, false);
+#endif
 
 		/* find all expressions that correspond to the column */
 		columnOperatorList = ColumnOperatorList(column, comparisonOperatorList);