Auto merge of #41588 - cengizIO:master, r=nikomatsakis

use diff crate for compile-fail test diagnostics #41474

Hello!

This fixes #41474

We were using a custom implementation to dump the differences between expected and actual outputs of compile-fail tests.

I removed this internal implementation and added `diff` crate as a new dependency to `compile-fail`.

Again, huge thanks to @nikomatsakis for guiding.

diff --cc src/Cargo.lock
Simple merge

diff --cc src/tools/compiletest/src/main.rs
Simple merge

diff --cc src/tools/compiletest/src/runtest.rs
index d38b1d61ddd94d6126c698e3b3e235d7d3c78a87,0bab518fccb8b5bc0cf27965f67a9ec098aba97e..731665ce034582770bb2ddf87967ebe4a9dc616b
--- 1/src/tools/compiletest/src/runtest.rs
--- 2/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@@ -16,9 -17,9 +17,8 @@@ use errors::{self, ErrorKind, Error}
  use filetime::FileTime;
  use json;
  use header::TestProps;
 -use header;
  use procsrv;
  use test::TestPaths;
- use uidiff;
  use util::logv;
  
  use std::collections::HashSet;