Add exit to example

Author: usbalbin

ci/expected/lm3s6965/spawn_local.run

@@ -0,0 +1,2 @@
+Hello from task1!
+Hello from task2!

examples/lm3s6965/examples/spawn_local.rs

@@ -5,7 +5,7 @@ use panic_semihosting as _;
 
 #[rtic::app(device = lm3s6965, dispatchers = [SSI0])]
 mod app {
-    use cortex_m_semihosting::hprintln;
+    use cortex_m_semihosting::{debug, hprintln};
     use super::*;
 
     #[shared]
@@ -25,18 +25,12 @@ mod app {
     async fn task1(cx: task1::Context) {
         hprintln!("Hello from task1!");
         cx.local_spawner.task2(Default::default()).unwrap();
-        cx.local_spawner.task3(Default::default()).unwrap();
     }
 
     #[task(priority = 1, local_task = true)]
     async fn task2(_cx: task2::Context, _nsns: NotSendNotSync) {
         hprintln!("Hello from task2!");
-    }
-
-    // The value of `local_task` may be omitted and is in that case interpreted as `true`
-    #[task(priority = 1, local_task)]
-    async fn task3(_cx: task3::Context, _nsns: NotSendNotSync) {
-        hprintln!("Hello from task3!");
+        debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
     }
 }