Feature/port avr build check (#35)

* fix atmega168 build.

* remove time.h to solve AVR compile

* Add AVR build to CI for compile check

ports/atmega168/apdu.c

@@ -122,6 +122,7 @@ void apdu_handler(
                     handler_unrecognized_service(service_request,
                         service_request_len, src, &service_data);
                 }
+                (void)len;
                 break;
             case PDU_TYPE_UNCONFIRMED_SERVICE_REQUEST:
                 service_choice = apdu[1];

ports/atmega168/h_rp.c

@@ -154,6 +154,7 @@ void handler_read_property(
     bytes_sent =
         datalink_send_pdu(src, &npdu_data, &Handler_Transmit_Buffer[0],
         pdu_len);
+    (void)bytes_sent;
 
     return;
 }

ports/atmega168/h_wp.c

@@ -133,6 +133,7 @@ void handler_write_property(
     bytes_sent =
         datalink_send_pdu(src, &npdu_data, &Handler_Transmit_Buffer[0],
         pdu_len);
+    (void)bytes_sent;
 
     return;
 }

ports/atmega168/rs485.c

@@ -260,7 +260,7 @@ bool RS485_ReceiveError(
     void)
 {
     bool ReceiveError = false;
-    uint8_t dummy_data;
+    volatile uint8_t dummy_data;
 
     /* check for framing error */
 #if 0
@@ -281,6 +281,7 @@ bool RS485_ReceiveError(
     if (ReceiveError) {
         RS485_LED1_On();
     }
+    (void)dummy_data;
 
     return ReceiveError;
 }