Add build test for forced single USB modes.

Fix UC3 Interrupt Management platform driver not compiling under C++.

LUFA/Platform/UC3/InterruptManagement.c

@@ -28,6 +28,7 @@
   this software.
 */
 
+#define  __INCLUDE_FROM_INTMANAGEMENT_C
 #include "InterruptManagement.h"
 
 /** Interrupt vector table, containing the ISR to call for each interrupt group */

LUFA/Platform/UC3/InterruptManagement.h

@@ -84,9 +84,11 @@
 			typedef void (*InterruptHandlerPtr_t)(void);
 
 		/* External Variables: */
-			extern const void            EVBA_Table;
-			extern const uint32_t        Autovector_Table[];
+			#if defined(__INCLUDE_FROM_INTMANAGEMENT_C)
+				extern const void        EVBA_Table;
+			#endif
 			extern InterruptHandlerPtr_t InterruptHandlers[AVR32_INTC_NUM_INT_GRPS];
+			extern const uint32_t        Autovector_Table[];
 	#endif
 
 	/* Public Interface - May be used in end-application: */