Fix tdweb build.

tdactor/td/actor/ConcurrentScheduler.cpp

@@ -138,10 +138,12 @@ void ConcurrentScheduler::finish() {
 #endif
 
   if (ExitGuard::is_exited()) {
+#if !TD_THREAD_UNSUPPORTED && !TD_EVENTFD_UNSUPPORTED
     // prevent closing of schedulers from already killed by OS threads
     for (auto &thread : threads_) {
       thread.detach();
     }
+#endif
 
 #if TD_PORT_WINDOWS
     iocp_->interrupt_loop();