Fixed compile error when FIXED_CONTROL_ENDPOINT_SIZE compile time option was disabled, and a USE_*_DESCRIPTORS compile time option was not enabled on the AVR8s.

Add C++ compatibility to some header files currently missing extern "C" linkage.

LUFA/Drivers/USB/Core/USBInterrupt.h

@@ -44,7 +44,12 @@
 	/* Includes: */
 		#include "../../../Common/Common.h"
 		#include "USBMode.h"		
-		
+
+	/* Enable C linkage for C++ Compilers: */
+		#if defined(__cplusplus)
+			extern "C" {
+		#endif
+
 	/* Preprocessor Checks: */
 		#if !defined(__INCLUDE_FROM_USB_DRIVER)
 			#error Do not include this file directly. Include LUFA/Drivers/USB/USB.h instead.
@@ -57,5 +62,10 @@
 			#include "UC3/USBInterrupt_UC3.h"
 		#endif
 
+	/* Disable C linkage for C++ Compilers: */
+		#if defined(__cplusplus)
+			}
+		#endif
+
 #endif