NLL ICE on `*const_ptr()`

[`src/test/compile-fail/issue-20801.rs`](https://github.com/rust-lang/rust/blob/master/src/test/compile-fail/issue-20801.rs) ICEs using NLL:

```
error: internal compiler error: Accessing `(*_8)` with the kind `Write(Move)` shouldn't be possible
  --> $DIR/issue-20801.rs:45:22
   |
LL |     let d = unsafe { *const_ptr() };
   |                      ^^^^^^^^^^^^
```