Don't free-up file-descriptor of stdin/stdout/stderr

stdout, stdin and stderr are statically allocated at tinystdio/posixiob_stdout.c, tinystdio/posixiob_stdin.c
and tinystdio/posixiob_stderr.c respectively.

and the issue here is that the current implementation of `fclose()` frees the allocated memory for the stream file.
When we call `fclose(stdout)` it tries to free an unallocated memory for _stdout_,
so it frees a wrong pointer and saves it as a free heap space, then when trying to use this memory it causes memory corruption.

So, we shouldn't free the memory if the stream is stdin, stdout or stderr.

newlib/libc/tinystdio/bufio.c

@@ -307,7 +307,10 @@ __bufio_close(FILE *f)
 	/* Don't close stdin/stdout/stderr fds */
 	if (bf->fd > 2)
 		(bf->close)(bf->fd);
-	free(f);
+
+        /* Don't free memory if the stream is stdin/stdout/stderr */
+        if ((f != stdin) && (f != stdout) && (f != stderr))
+		free(f);
 	return ret;
 }