auto merge of #10588 : huonw/rust/un@mutilate-task_rng, r=alexcrichton

Replace with some unsafe code by storing a pointer into TLS-owned heap
data.

src/test/compile-fail/task-rng-isnt-sendable.rs

@@ -0,0 +1,18 @@
+// Copyright 2013 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.
+
+// ensure that the TaskRng isn't/doesn't become accidentally sendable.
+
+fn test_send<S: Send>() {}
+
+pub fn main() {
+    test_send::<::std::rand::TaskRng>();
+    //~^ ERROR: incompatible type `std::rand::TaskRng`, which does not fulfill `Send`
+}