[testcase][thread_tc]修复高优化等级时thread测试用例死循环的问题 (#7483)

examples/utest/testcases/kernel/thread_tc.c

@@ -28,10 +28,10 @@ static struct rt_thread thread2;
     static rt_thread_t tid7 = RT_NULL;
 #endif /* RT_USING_HEAP */
 
-static rt_uint32_t tid3_delay_pass_flag = 0;
-static rt_uint32_t tid3_finish_flag = 0;
-static rt_uint32_t tid4_finish_flag = 0;
-static rt_uint32_t tid6_finish_flag = 0;
+static volatile rt_uint32_t tid3_delay_pass_flag = 0;
+static volatile rt_uint32_t tid3_finish_flag = 0;
+static volatile rt_uint32_t tid4_finish_flag = 0;
+static volatile rt_uint32_t tid6_finish_flag = 0;
 static rt_uint32_t thread5_source = 0;
 
 #ifndef RT_USING_SMP