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

fusl/src/locale/wcsxfrm.c

+#include <wchar.h>
+#include <locale.h>
+#include "locale_impl.h"
+#include "libc.h"
+
+/* collate only by code points */
+size_t __wcsxfrm_l(wchar_t *restrict dest, const wchar_t *restrict src, size_t n, locale_t loc)
+{
+        size_t l = wcslen(src);
+        if (l < n) {
+                wmemcpy(dest, src, l+1);
+        } else if (n) {
+                wmemcpy(dest, src, n-1);
+                dest[n-1] = 0;
+        }
+        return l;
+}
+
+size_t wcsxfrm(wchar_t *restrict dest, const wchar_t *restrict src, size_t n)
+{
+        return __wcsxfrm_l(dest, src, n, CURRENT_LOCALE);
+}
+
+weak_alias(__wcsxfrm_l, wcsxfrm_l);