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

fusl/src/thread/pthread_rwlock_timedrdlock.c

Index: fusl/src/thread/pthread_rwlock_timedrdlock.c
diff --git a/fusl/src/thread/pthread_rwlock_timedrdlock.c b/fusl/src/thread/pthread_rwlock_timedrdlock.c
new file mode 100644
index 0000000000000000000000000000000000000000..0d5d0d6c05fe8fe5c93999d45dbd76b47ee860b1
--- /dev/null
+++ b/fusl/src/thread/pthread_rwlock_timedrdlock.c
@@ -0,0 +1,23 @@
+#include "pthread_impl.h"
+
+int pthread_rwlock_timedrdlock(pthread_rwlock_t *restrict rw, const struct timespec *restrict at)
+{
+	int r, t;
+
+	r = pthread_rwlock_tryrdlock(rw);
+	if (r != EBUSY) return r;
+	
+	int spins = 100;
+	while (spins-- && rw->_rw_lock && !rw->_rw_waiters) a_spin();
+
+	while ((r=pthread_rwlock_tryrdlock(rw))==EBUSY) {
+		if (!(r=rw->_rw_lock) || (r&0x7fffffff)!=0x7fffffff) 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;
+}