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

fusl/src/legacy/ftw.c

+#include <ftw.h>
+#include "libc.h"
+
+int ftw(const char *path, int (*fn)(const char *, const struct stat *, int), int fd_limit)
+{
+        /* The following cast assumes that calling a function with one
+         * argument more than it needs behaves as expected. This is
+         * actually undefined, but works on all real-world machines. */
+        return nftw(path, (int (*)())fn, fd_limit, FTW_PHYS);
+}
+
+LFS64(ftw);