emulator: run cleanup handlers on the quick_exit path (#334)

Run() registers KytyClose with atexit(), but Execute() ends the process with
std::quick_exit(), which invokes at_quick_exit handlers only. Nothing registered
one, so the cleanup never ran and neither did the emergency shutdown handlers
that close open guest files and flush the log.

Register a quick-exit handler that runs the emergency shutdown. It deliberately
skips RuntimeLinker::Clear(): guest threads are still live at that point and
tearing the linker down there deadlocks against a thread parked in a condition
wait.

src/emulator.cpp

@@ -200,6 +200,10 @@ void Run(const RunOptions& options) {
 	int ok = atexit(KytyClose);
 	EXIT_NOT_IMPLEMENTED(ok != 0);
 
+	// Guest threads are still running, so skip KytyClose() and only flush emergency state.
+	ok = at_quick_exit(Common::Subsystems::EmergencyShutdownActive);
+	EXIT_NOT_IMPLEMENTED(ok != 0);
+
 	Libs::LibKernel::FileSystem::Mount(options.app0_dir, "/app0");
 	Libs::LibKernel::FileSystem::Mount(options.app0_dir, "/hostapp");