rework structure

hifive1-vp/hello/bsp/libwrap/sys/fstat.c

@@ -0,0 +1,16 @@
+/* See LICENSE of license details. */
+
+#include <errno.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include "stub.h"
+
+int __wrap_fstat(int fd, struct stat* st)
+{
+  if (isatty(fd)) {
+    st->st_mode = S_IFCHR;
+    return 0;
+  }
+
+  return _stub(EBADF);
+}