Add tests to fixed ICEs

Closes #27078. Closes #27985. Closes #39848. Closes #42164.
Closes #42479. Closes #45152. Closes #45662. Closes #45876.
Closes #45965.

src/test/run-pass/impl-trait/issue-42479.rs

@@ -0,0 +1,27 @@
+// Copyright 2017 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.
+
+#![feature(conservative_impl_trait)]
+
+use std::iter::once;
+
+struct Foo {
+    x: i32,
+}
+
+impl Foo {
+    fn inside(&self) -> impl Iterator<Item = &i32> {
+        once(&self.x)
+    }
+}
+
+fn main() {
+    println!("hi");
+}