Auto merge of #28069 - alexcrichton:rt-atexit, r=brson

This adds a call to `rt::cleanup` on `process::exit` to make sure we clean up
after ourselves on the way out from Rust.

Closes #28065

src/test/run-pass/exit-flushes.rs

@@ -0,0 +1,25 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::env;
+use std::process::{exit, Command};
+
+fn main() {
+    if env::args().len() > 1 {
+        print!("hello!");
+        exit(0);
+    } else {
+        let out = Command::new(env::args().next().unwrap()).arg("foo")
+                          .output().unwrap();
+        assert!(out.status.success());
+        assert_eq!(String::from_utf8(out.stdout).unwrap(), "hello!");
+        assert_eq!(String::from_utf8(out.stderr).unwrap(), "");
+    }
+}