Merge pull request #2849 from enkiller/idle

[src][idle] 修复一处编译警告

src/idle.c

@@ -55,7 +55,7 @@ static rt_uint8_t rt_thread_stack[_CPUS_NR][IDLE_THREAD_STACK_SIZE];
 #define RT_IDEL_HOOK_LIST_SIZE  4
 #endif
 
-static void (*idle_hook_list[RT_IDEL_HOOK_LIST_SIZE])();
+static void (*idle_hook_list[RT_IDEL_HOOK_LIST_SIZE])(void);
 
 /**
  * @ingroup Hook