添加rtthread相关代码

riscv/rtthread/components/libc/posix/libdl/dlerror.c

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2006-2021, RT-Thread Development Team
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Change Logs:
+ * Date           Author      Notes
+ * 2010-11-17     yi.qiu      first version
+ */
+
+#include <rtthread.h>
+#include <rtm.h>
+
+const char *dlerror(void)
+{
+    return "TODO";
+}
+RTM_EXPORT(dlerror)