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

fusl/src/thread/pthread_rwlock_timedwrlock.c

Index: fusl/src/thread/pthread_rwlock_timedwrlock.c
diff --git a/fusl/src/thread/pthread_rwlock_timedwrlock.c b/fusl/src/thread/pthread_rwlock_timedwrlock.c
new file mode 100644
index 0000000000000000000000000000000000000000..7f26dad1f5915e8cf5f81f6a39e9695a071d5005
--- /dev/null
+++ b/fusl/src/thread/pthread_rwlock_timedwrlock.c
@@ -0,0 +1,23 @@
+#include "pthread_impl.h"
+
+int pthread_rwlock_timedwrlock(pthread_rwlock_t *restrict rw, const struct timespec *restrict at)
+{
+	int r, t;
+	
+	r = pthread_rwlock_trywrlock(rw);
+	if (r != EBUSY) return r;
+	
+	int spins = 100;
+	while (spins-- && rw->_rw_lock && !rw->_rw_waiters) a_spin();
+
+	while ((r=pthread_rwlock_trywrlock(rw))==EBUSY) {
+		if (!(r=rw->_rw_lock)) continue;
+		t = r | 0x80000000;
+		a_inc(&rw->_rw_waiters);
+		a_cas(&rw->_rw_lock, r, t);
+		r = __timedwait(&rw->_rw_lock, t, CLOCK_REALTIME, at, rw->_rw_shared^128);
+		a_dec(&rw->_rw_waiters);
+		if (r && r != EINTR) return r;
+	}
+	return r;
+}