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

fusl/src/thread/pthread_detach.c

+#include "pthread_impl.h"
+#include <threads.h>
+
+int __pthread_join(pthread_t, void **);
+
+static int __pthread_detach(pthread_t t)
+{
+        /* Cannot detach a thread that's already exiting */
+        if (a_swap(t->exitlock, 1))
+                return __pthread_join(t, 0);
+        t->detached = 2;
+        __unlock(t->exitlock);
+        return 0;
+}
+
+weak_alias(__pthread_detach, pthread_detach);
+weak_alias(__pthread_detach, thrd_detach);