Move check for devices not supporting internal serials in demos which make use of USE_INTERNAL_SERIAL to Descriptors.c from Descriptors.h so that the warning is only generated at most once per compilation.

Demos/Device/ClassDriver/DualCDC/Descriptors.c

@@ -37,6 +37,18 @@
 
 #include "Descriptors.h"
 
+/* On some devices, there is a factory set internal serial number which can be automatically sent to the host as
+ * the device's serial number when the Device Descriptor's .SerialNumStrIndex entry is set to USE_INTERNAL_SERIAL.
+ * This allows the host to track a device across insertions on different ports, allowing them to retain allocated
+ * resources like COM port numbers and drivers. On demos using this feature, give a warning on unsupported devices
+ * so that the user can supply their own serial number descriptor instead or remove the USE_INTERNAL_SERIAL value
+ * from the Device Descriptor (forcing the host to generate a serial number for each device from the VID, PID and
+ * port location).
+ */
+#if (USE_INTERNAL_SERIAL == NO_DESCRIPTOR)
+	#warning USE_INTERNAL_SERIAL is not available on this AVR - please manually construct a device serial descriptor.
+#endif
+
 /** Device descriptor structure. This descriptor, located in FLASH memory, describes the overall
  *  device characteristics, including the supported USB version, control endpoint size and the
  *  number of device configurations. The descriptor is read out by the USB host when the enumeration

Demos/Device/ClassDriver/DualCDC/Descriptors.h

@@ -42,10 +42,6 @@
 		#include <LUFA/Drivers/USB/USB.h>
 		#include <LUFA/Drivers/USB/Class/CDC.h>
 
-		#if (USE_INTERNAL_SERIAL == NO_DESCRIPTOR)
-			#warning USE_INTERNAL_SERIAL is not available on this AVR - please manually construct a device serial descriptor.
-		#endif
-
 	/* Macros: */
 		/** Endpoint number of the first CDC interface's device-to-host notification IN endpoint. */
 		#define CDC1_NOTIFICATION_EPNUM        3