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

fusl/src/locale/uselocale.c

Index: fusl/src/locale/uselocale.c
diff --git a/fusl/src/locale/uselocale.c b/fusl/src/locale/uselocale.c
new file mode 100644
index 0000000000000000000000000000000000000000..0fc5ecbc07f29437e1afb66815074360bfd360cb
--- /dev/null
+++ b/fusl/src/locale/uselocale.c
@@ -0,0 +1,16 @@
+#include "locale_impl.h"
+#include "pthread_impl.h"
+#include "libc.h"
+
+locale_t __uselocale(locale_t new)
+{
+	pthread_t self = __pthread_self();
+	locale_t old = self->locale;
+	locale_t global = &libc.global_locale;
+
+	if (new) self->locale = new == LC_GLOBAL_LOCALE ? global : new;
+
+	return old == global ? LC_GLOBAL_LOCALE : old;
+}
+
+weak_alias(__uselocale, uselocale);