add noreturn attribute for LOS_Panic

Change-Id: Id2c76e3282d72bce18cf0925e12afaa0c3b06a90

arch/arm/arm/src/los_exc.c

@@ -1138,6 +1138,7 @@ __attribute__((noinline)) VOID LOS_Panic(const CHAR *fmt, ...)
     UartVprintf(fmt, ap);
     va_end(ap);
     __asm__ __volatile__("swi 0");
+    while (1);
 }
 
 /* stack protector */

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, ...);
+VOID LOS_Panic(const CHAR *fmt, ...) __attribute__ ((noreturn));
 
 /**
  * @ingroup los_exc