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

fusl/src/thread/sem_post.c

+#include <semaphore.h>
+#include "pthread_impl.h"
+
+int sem_post(sem_t *sem)
+{
+        int val, waiters, priv = sem->__val[2];
+        do {
+                val = sem->__val[0];
+                waiters = sem->__val[1];
+                if (val == SEM_VALUE_MAX) {
+                        errno = EOVERFLOW;
+                        return -1;
+                }
+        } while (a_cas(sem->__val, val, val+1+(val<0)) != val);
+        if (val<0 || waiters) __wake(sem->__val, 1, priv);
+        return 0;
+}