Mrntt: Add ability to listen for SIGSEGV

But don't actually use it because it makes it difficult to
exit SMO from the cmdline.

smocore/marionette/marionette.cpp

@@ -49,12 +49,22 @@ void ComponentThread::marionetteMain(ComponentThread& self)
 	bool callFinalizeReq = false;
 
 	try {
-		// Register SIGINT (Ctrl+C) handler to request user shutdown
+		// Register SIGINT (Ctrl+C) and SIGSEGV handlers
 		signals.async_wait(
-			[&self](const boost::system::error_code& ec, int /*signal*/)
+			[&self](const boost::system::error_code& ec, int signal)
 			{
 				if (ec) { return; }
-				// Post user shutdown indication
+
+				switch (signal) {
+					case SIGINT:
+						std::cerr << "SIGINT (Ctrl+C) received. Initiating shutdown..." << std::endl;
+						break;
+					case SIGSEGV:
+						std::cerr << "FATAL: Segmentation fault detected. Initiating shutdown..." << std::endl;
+						break;
+					default:
+						break;
+				}
 				self.userShutdownInd();
 			}
 		);