unix/SignalHandlers: shut down if parent process dies in --no-daemon mode

By default, if the parent of a process dies, the process gets SIGHUP
and is supposed to shut down.  This however doesn't work for MPD,
because MPD redefines SIGHUP with a different meaning (like most
daemons do).

To work around this, we configure the kernel to send SIGTERM instead
of SIGHUP.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1706

src/Main.cxx

@@ -431,7 +431,10 @@ MainConfigured(const CommandLineOptions &options,
 #ifndef ANDROID
 	setup_log_output();
 
-	const ScopeSignalHandlersInit signal_handlers_init(instance);
+	const ScopeSignalHandlersInit signal_handlers_init{
+		instance,
+		options.daemon,
+	};
 #endif
 
 	instance.io_thread.Start();