Add a "fork" of musl as //fusl.

fusl/src/dirent/readdir_r.c

Index: fusl/src/dirent/readdir_r.c
diff --git a/fusl/src/dirent/readdir_r.c b/fusl/src/dirent/readdir_r.c
new file mode 100644
index 0000000000000000000000000000000000000000..daa6c6ed608449051ae46fcf800fa521dbc24fa1
--- /dev/null
+++ b/fusl/src/dirent/readdir_r.c
@@ -0,0 +1,29 @@
+#include <dirent.h>
+#include <errno.h>
+#include <string.h>
+#include "__dirent.h"
+#include "libc.h"
+
+int readdir_r(DIR *restrict dir, struct dirent *restrict buf, struct dirent **restrict result)
+{
+	struct dirent *de;
+	int errno_save = errno;
+	int ret;
+	
+	LOCK(dir->lock);
+	errno = 0;
+	de = readdir(dir);
+	if ((ret = errno)) {
+		UNLOCK(dir->lock);
+		return ret;
+	}
+	errno = errno_save;
+	if (de) memcpy(buf, de, de->d_reclen);
+	else buf = NULL;
+
+	UNLOCK(dir->lock);
+	*result = buf;
+	return 0;
+}
+
+LFS64_2(readdir_r, readdir64_r);