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

fusl/src/thread/pthread_detach.c

Index: fusl/src/thread/pthread_detach.c
diff --git a/fusl/src/thread/pthread_detach.c b/fusl/src/thread/pthread_detach.c
new file mode 100644
index 0000000000000000000000000000000000000000..ed77f74d520bff3a16ef5e055f08bbf021fe91d4
--- /dev/null
+++ b/fusl/src/thread/pthread_detach.c
@@ -0,0 +1,17 @@
+#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);