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

fusl/src/legacy/ftw.c

Index: fusl/src/legacy/ftw.c
diff --git a/fusl/src/legacy/ftw.c b/fusl/src/legacy/ftw.c
new file mode 100644
index 0000000000000000000000000000000000000000..0429aba495d0d5fca18945bc1607b1a65078589c
--- /dev/null
+++ b/fusl/src/legacy/ftw.c
@@ -0,0 +1,12 @@
+#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);