[example] 对版权信息进行人工扫描并添加确实的版权信息

examples/libc/ex4.c

@@ -1,3 +1,11 @@
+/*
+ * Copyright (c) 2006-2021, RT-Thread Development Team
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Change Logs:
+ * Date           Author       Notes
+ */
 /* Making a library function that uses static variables thread-safe.
    Illustrates: thread-specific data, pthread_once(). */