Process termination tests

Related issues:
- https://github.com/fortanix/rust-sgx/issues/109

src/test/ui/process-termination/process-termination-blocking-io.rs

@@ -0,0 +1,18 @@
+// program should terminate even if a thread is blocked on I/O.
+// https://github.com/fortanix/rust-sgx/issues/109
+
+// run-pass
+
+use std::{net::TcpListener, sync::mpsc, thread};
+
+fn main() {
+    let (tx, rx) = mpsc::channel();
+    thread::spawn(move || {
+        let listen = TcpListener::bind("0:0").unwrap();
+        tx.send(()).unwrap();
+        while let Ok(_) = listen.accept() {}
+    });
+    rx.recv().unwrap();
+    for _ in 0..3 { thread::yield_now(); }
+    println!("Exiting main thread");
+}

src/test/ui/process-termination/process-termination-simple.rs

@@ -0,0 +1,12 @@
+// program should terminate when std::process::exit is called from any thread
+
+// run-pass
+
+use std::{process, thread};
+
+fn main() {
+    let h = thread::spawn(|| {
+        process::exit(0);
+    });
+    let _ = h.join();
+}