Add error message (i.e. do not ICE) when moving out of unsafe pointers.

Fix #20801.

src/test/compile-fail/issue-20801.rs

@@ -0,0 +1,47 @@
+// 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.
+
+// We used to ICE when moving out of a `*mut T` or `*const T`.
+
+struct T(u8);
+
+static mut GLOBAL_MUT_T: T = T(0);
+
+static GLOBAL_T: T = T(0);
+
+fn imm_ref() -> &'static T {
+    unsafe { &GLOBAL_T }
+}
+
+fn mut_ref() -> &'static mut T {
+    unsafe { &mut GLOBAL_MUT_T }
+}
+
+fn mut_ptr() -> *mut T {
+    unsafe { 0u8 as *mut T }
+}
+
+fn const_ptr() -> *const T {
+    unsafe { 0u8 as *const T }
+}
+
+pub fn main() {
+    let a = unsafe { *mut_ref() };
+    //~^ ERROR cannot move out of dereference of borrowed content
+
+    let b = unsafe { *imm_ref() };
+    //~^ ERROR cannot move out of dereference of borrowed content
+
+    let c = unsafe { *mut_ptr() };
+    //~^ ERROR cannot move out of dereference of unsafe pointer
+
+    let d = unsafe { *const_ptr() };
+    //~^ ERROR cannot move out of dereference of unsafe pointer
+}