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

fusl/src/ctype/iswxdigit.c

Index: fusl/src/ctype/iswxdigit.c
diff --git a/fusl/src/ctype/iswxdigit.c b/fusl/src/ctype/iswxdigit.c
new file mode 100644
index 0000000000000000000000000000000000000000..1e27f1f0f9d82dc1b70d6d65ec917358dedf839d
--- /dev/null
+++ b/fusl/src/ctype/iswxdigit.c
@@ -0,0 +1,14 @@
+#include <wctype.h>
+#include "libc.h"
+
+int iswxdigit(wint_t wc)
+{
+	return (unsigned)(wc-'0') < 10 || (unsigned)((wc|32)-'a') < 6;
+}
+
+int __iswxdigit_l(wint_t c, locale_t l)
+{
+	return iswxdigit(c);
+}
+
+weak_alias(__iswxdigit_l, iswxdigit_l);