Fix task system dignostic to report real reason of the symaphore allocation fail

examples/tasksys.cpp

@@ -696,7 +696,7 @@ InitTaskSystem() {
                     sprintf(name, "ispc_task.%d", (int)getpid());
                     workerSemaphore = sem_open(name, O_CREAT, S_IRUSR|S_IWUSR, 0);
                     if (!workerSemaphore) {
-                        fprintf(stderr, "Error creating semaphore: %s\n", strerror(err));
+                        fprintf(stderr, "Error creating semaphore (%s): %s\n", name, strerror(errno));
                         exit(1);
                     }