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

fusl/src/thread/pthread_mutex_timedlock.c

+#include "pthread_impl.h"
+
+int __pthread_mutex_timedlock(pthread_mutex_t *restrict m, const struct timespec *restrict at)
+{
+        if ((m->_m_type&15) == PTHREAD_MUTEX_NORMAL
+            && !a_cas(&m->_m_lock, 0, EBUSY))
+                return 0;
+
+        int r, t, priv = (m->_m_type & 128) ^ 128;
+
+        r = pthread_mutex_trylock(m);
+        if (r != EBUSY) return r;
+        
+        int spins = 100;
+        while (spins-- && m->_m_lock && !m->_m_waiters) a_spin();
+
+        while ((r=pthread_mutex_trylock(m)) == EBUSY) {
+                if (!(r=m->_m_lock) || ((r&0x40000000) && (m->_m_type&4)))
+                        continue;
+                if ((m->_m_type&3) == PTHREAD_MUTEX_ERRORCHECK
+                 && (r&0x7fffffff) == __pthread_self()->tid)
+                        return EDEADLK;
+
+                a_inc(&m->_m_waiters);
+                t = r | 0x80000000;
+                a_cas(&m->_m_lock, r, t);
+                r = __timedwait(&m->_m_lock, t, CLOCK_REALTIME, at, priv);
+                a_dec(&m->_m_waiters);
+                if (r && r != EINTR) break;
+        }
+        return r;
+}
+
+weak_alias(__pthread_mutex_timedlock, pthread_mutex_timedlock);