Followed Steve's good recommendation, and made routed_get_my_address() be a variant of datalink_get_my_address() just when routing is in use. Haven't done anything about the sending functions yet.

Renamed Lookup_Routed_Device_Address() as Routed_Device_Address_Lookup(), and replaced it in the routed npdu handler with a function that finds the "next" gateway or routed device, as per the destination address.  (Less tied to the specifics of the gw_device.c implementation.)
Fixed a few build warnings (eg, %zu for size_t arguments).
Until we improve the makefile system, I've enabled BAC_ROUTING in config.h

bacnet-stack/demo/handler/h_arf.c

@@ -118,11 +118,7 @@ void handler_atomic_read_file(
     fprintf(stderr, "Received Atomic-Read-File Request!\n");
 #endif
     /* encode the NPDU portion of the packet */
-#if BAC_ROUTING
-    my_address = *Get_Routed_Device_Address(-1);
-#else
     datalink_get_my_address(&my_address);
-#endif
     npdu_encode_npdu_data(&npdu_data, false, MESSAGE_PRIORITY_NORMAL);
     pdu_len =
         npdu_encode_pdu(&Handler_Transmit_Buffer[0], src, &my_address,
@@ -174,7 +170,7 @@ void handler_atomic_read_file(
                     service_data->invoke_id,
                     ABORT_REASON_SEGMENTATION_NOT_SUPPORTED, true);
 #if PRINT_ENABLED
-                fprintf(stderr, "Too Big To Send (%d >= %d). Sending Abort!\n",
+                fprintf(stderr, "Too Big To Send (%d >= %zu). Sending Abort!\n",
                     data.type.stream.requestedOctetCount,
                     octetstring_capacity(&data.fileData));
 #endif