Removed fibers from compilation.

It's not used anyway, but breaks building with musl.

This closes issue #5 on GitHub.

src/nxt_runtime.c

@@ -292,7 +292,9 @@ nxt_runtime_event_engines(nxt_task_t *task, nxt_runtime_t *rt)
 
     thread = task->thread;
     thread->engine = engine;
+#if 0
     thread->fiber = &engine->fibers->fiber;
+#endif
 
     engine->id = rt->last_engine_id++;