Make debug prints portable (#929)

hal/architecture/MyHwAVR.cpp

@@ -317,7 +317,7 @@ void hwDebugPrint(const char *fmt, ... )
 	char fmtBuffer[MY_SERIAL_OUTPUT_SIZE];
 #ifdef MY_GATEWAY_SERIAL
 	// prepend debug message to be handled correctly by controller (C_INTERNAL, I_LOG_MESSAGE)
-	snprintf_P(fmtBuffer, sizeof(fmtBuffer), PSTR("0;255;%d;0;%d;%lu "),
+	snprintf_P(fmtBuffer, sizeof(fmtBuffer), PSTR("0;255;%" PRIu8 ";0;%" PRIu8 ";%" PRIu32 " "),
 	           C_INTERNAL, I_LOG_MESSAGE, hwMillis());
 	MY_SERIALDEVICE.print(fmtBuffer);
 #else
@@ -336,5 +336,7 @@ void hwDebugPrint(const char *fmt, ... )
 	va_end (args);
 	MY_SERIALDEVICE.print(fmtBuffer);
 	MY_SERIALDEVICE.flush();
+#else
+	(void)fmt;
 #endif
 }