!174 将NORETURN声明放到函数前，KEIL不支持放在函数后

Merge pull request !174 from Caoruihong/fix_noreturn

arch/arm/include/los_exc.h

@@ -183,7 +183,7 @@ extern UINT32 LOS_ExcRegHook(EXC_PROC_FUNC excHook);
  * los_exc.h: the header file that contains the API declaration.
  * @see None.
  */
-VOID LOS_Panic(const CHAR *fmt, ...) NORETURN;
+NORETURN VOID LOS_Panic(const CHAR *fmt, ...);
 
 /**
  * @ingroup los_exc