main: Add wait_signal function

Moving the signal handler setup and wait to a separate function will
allow us to eventually create platform-specific implementations.
Windows doesn't have SIGINT/SIGTERM, so we will need different logic if
we ever want to support that OS.

src/main.rs

@@ -21,18 +21,23 @@ async fn main() {
         config::load_config(std::env::var("MQTTMARIONETTE_CONFIG").ok())
             .unwrap();
 
-    let mut sig_term = unix::signal(SignalKind::terminate()).unwrap();
-    let mut sig_int = unix::signal(SignalKind::interrupt()).unwrap();
-
     let task = tokio::spawn(async move {
         let session = Session::begin(config).await.unwrap();
         session.run().await;
     });
 
+    wait_signal().await;
+
+    task.abort();
+}
+
+#[cfg(unix)]
+async fn wait_signal() {
+    let mut sig_term = unix::signal(SignalKind::terminate()).unwrap();
+    let mut sig_int = unix::signal(SignalKind::interrupt()).unwrap();
+
     tokio::select! {
         _ = sig_term.recv() => info!("Received SIGTERM"),
         _ = sig_int.recv() => info!("Received SIGINT"),
     };
-
-    task.abort();
 }