[ScheduleOnTest] block worker thread if IO is not available

The alpha fiber waits to ensure the worker threads are suspended before starting to schedule work on specific threads. emper::sleep uses an AlarmFuture and thus needs emper to be build with IO support. If IO is not available we now just block the whole worker thread.

tests/ScheduleOnTest.cpp

 // SPDX-License-Identifier: LGPL-3.0-or-later
 // Copyright © 2021 Florian Fischer
+#include <chrono>
+#include <thread>
+
 #include "CountingPrivateSemaphore.hpp"
+#include "Emper.hpp"
 #include "Fiber.hpp"
 #include "Runtime.hpp"
 #include "Worker.hpp"
@@ -25,7 +29,12 @@ static void scheduleOnTest() {
 	ASSERT(runtime);
 	workerCount = runtime->getWorkerCount();
 
-	emper::sleep(1);
+	// Wait so all workers can suspend themselves
+	if constexpr (emper::IO) {
+		emper::sleep(1);
+	} else {	// We can not sleep using emper mechanisms -> block the worker thread
+		std::this_thread::sleep_for(std::chrono::seconds(1));
+	}
 
 	CPS cps(1);
 	runtime->scheduleOn(*Fiber::from([&] { runOn(cps); }), (iteration % workerCount));