score/cpu/moxie/.../cpu.h: Address unused variable warning

The Moxie does not implement the interrupt disable/enable functions
and this led to an unused variable warning. Just added proper
annotation to let GCC know it is intentionally unused.

cpukit/score/cpu/moxie/include/rtems/score/cpu.h

@@ -319,6 +319,8 @@ typedef struct {
 
 static inline bool _CPU_ISR_Is_enabled( uint32_t level )
 {
+  (void) level;
+
   return true;
 }