Auto merge of #2519 - saethlin:rustup, r=RalfJung

Use the better FnEntry spans in protector errors

Example error, from `tests/fail/stacked_borrows/invalidate_against_protector1.rs`:
```
error: Undefined Behavior: not granting access to tag <3095> because that would remove [Unique for <3099>] which is protected because it is an argument of call 943
  --> tests/fail/stacked_borrows/invalidate_against_protector1.rs:5:25
   |
5  |     let _val = unsafe { *x }; //~ ERROR: protect
   |                         ^^ not granting access to tag <3095> because that would remove [Unique for <3099>] which is protected because it is an argument of call 943
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <3095> was created by a SharedReadWrite retag at offsets [0x0..0x4]
  --> tests/fail/stacked_borrows/invalidate_against_protector1.rs:10:16
   |
10 |     let xraw = &mut x as *mut _;
   |                ^^^^^^
help: <3099> is this argument
  --> tests/fail/stacked_borrows/invalidate_against_protector1.rs:1:23
   |
1  | fn inner(x: *mut i32, _y: &mut i32) {
   |                       ^^
   = note: backtrace:
   = note: inside `inner` at tests/fail/stacked_borrows/invalidate_against_protector1.rs:5:25
note: inside `main` at tests/fail/stacked_borrows/invalidate_against_protector1.rs:12:5
  --> tests/fail/stacked_borrows/invalidate_against_protector1.rs:12:5
   |
12 |     inner(xraw, xref);
   |     ^^^^^^^^^^^^^^^^^
```

Benchmarks report no change, within noise.

0 files changed, 0 insertions, 0 deletions