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

fusl/src/locale/duplocale.c

Index: fusl/src/locale/duplocale.c
diff --git a/fusl/src/locale/duplocale.c b/fusl/src/locale/duplocale.c
new file mode 100644
index 0000000000000000000000000000000000000000..030b64cb0e706cdf29c7104526e86b6ee08d7adb
--- /dev/null
+++ b/fusl/src/locale/duplocale.c
@@ -0,0 +1,15 @@
+#include <stdlib.h>
+#include <string.h>
+#include "locale_impl.h"
+#include "libc.h"
+
+locale_t __duplocale(locale_t old)
+{
+	locale_t new = malloc(sizeof *new);
+	if (!new) return 0;
+	if (old == LC_GLOBAL_LOCALE) old = &libc.global_locale;
+	*new = *old;
+	return new;
+}
+
+weak_alias(__duplocale, duplocale);