Explicit switch/case fallthroughs to avoid compiler warnings.

src/backend/distributed/relay/relay_event_utility.c

@@ -164,6 +164,7 @@ RelayEventExtendNames(Node *parseTree, char *schemaName, uint64 shardId)
 			 * performed on CreateStmt should be done here too, we simply *fall
 			 * through* to avoid code repetition.
 			 */
+			__attribute__((fallthrough));
 		}
 
 		case T_CreateStmt:

src/backend/distributed/utils/ruleutils_96.c

@@ -4449,6 +4449,7 @@ isSimpleNode(Node *node, Node *parentNode, int prettyFlags)
 				}
 				/* else do the same stuff as for T_SubLink et al. */
 				/* FALL THROUGH */
+				__attribute__((fallthrough));
 			}
 
 		case T_SubLink: