Add ICE regression test with unboxed closures

This code used to produce the following ICE:

   error: internal compiler error: get_unique_type_id_of_type() -
   unexpected type: closure,
   ty_unboxed_closure(syntax::ast::DefId{krate: 0u32, node: 66u32},
   ReScope(63u32))

This is a regression test for issue #17021.

src/test/run-pass/unboxed-closures-unique-type-id.rs

@@ -0,0 +1,34 @@
+// Copyright 2012 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.
+//
+// This code used to produce the following ICE:
+//
+//    error: internal compiler error: get_unique_type_id_of_type() -
+//    unexpected type: closure,
+//    ty_unboxed_closure(syntax::ast::DefId{krate: 0u32, node: 66u32},
+//    ReScope(63u32))
+//
+// This is a regression test for issue #17021.
+
+#![feature(unboxed_closures, overloaded_calls)]
+
+use std::ptr;
+
+pub fn replace_map<'a, T, F>(src: &mut T, prod: F)
+where F: |: T| -> T {
+    unsafe { *src = prod(ptr::read(src as *mut T as *const T)); }
+}
+
+pub fn main() {
+    let mut a = 7u;
+    let b = &mut a;
+    replace_map(b, |: x: uint| x * 2);
+    assert_eq!(*b, 14u);
+}