Rollup merge of #49730 - sinkuu:fix_ice_49556, r=cramertj

Fix ICE with impl Trait

Fixes https://github.com/rust-lang/rust/issues/49556#issuecomment-379154713. May or may not fix 49556 itself. Closures like `|x: &'a _| x` has `ClosureSubsts` of `fn(&'a _) -> &'(ReScope) _`, so `tcx.note_and_explain_free_region` (called [here](a143462783/src/librustc/infer/anon_types/mod.rs (L572))) panics.

src/test/run-pass/issue-49556.rs

@@ -0,0 +1,22 @@
+// Copyright 2018 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.
+
+fn iter<'a>(data: &'a [usize]) -> impl Iterator<Item = usize> + 'a {
+    data.iter()
+        .map(
+            |x| x // fn(&'a usize) -> &'(ReScope) usize
+        )
+        .map(
+            |x| *x // fn(&'(ReScope) usize) -> usize
+        )
+}
+
+fn main() {
+}