Auto merge of #8559 - ehuss:fix-lto-tests-flaky, r=alexcrichton

Auto merge of #8559 - ehuss:fix-lto-tests-flaky, r=alexcrichton

Fix sporadic lto test failures.

These tests can fail because the order of the messages is not deterministic.  The two `foo` jobs start in parallel, so the order can be swapped.  Results in an error like:

```
---- lto::test_profile stdout ----
running `/home/runner/work/cargo/cargo/target/debug/cargo test -v`
thread 'lto::test_profile' panicked at '
Expected: execs
    but: differences:
  6 - |[RUNNING] `rustc --crate-name foo [..]--crate-type lib --emit=dep-info,metadata,link -Cembed-bitcode=no[..]|
    + |     Running `rustc --crate-name foo --edition=2018 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --emit=dep-info,link -C lto=thin -C debuginfo=2 --test -C metadata=af771ad588185fac -C extra-filename=-af771ad588185fac --out-dir /home/runner/work/cargo/cargo/target/cit/t1080/foo/target/debug/deps -L dependency=/home/runner/work/cargo/cargo/target/cit/t1080/foo/target/debug/deps --extern bar=/home/runner/work/cargo/cargo/target/cit/t1080/foo/target/debug/deps/libbar-398704963dd4e38b.rlib`|

  7 - |[RUNNING] `rustc --crate-name foo [..]--emit=dep-info,link -C lto=thin [..]--test[..]|
    + |     Running `rustc --crate-name foo --edition=2018 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type lib --emit=dep-info,metadata,link -Cembed-bitcode=no -C debuginfo=2 -C metadata=1e8f5d385f4ffeb6 -C extra-filename=-1e8f5d385f4ffeb6 --out-dir /home/runner/work/cargo/cargo/target/cit/t1080/foo/target/debug/deps -L dependency=/home/runner/work/cargo/cargo/target/cit/t1080/foo/target/debug/deps --extern bar=/home/runner/work/cargo/cargo/target/cit/t1080/foo/target/debug/deps/libbar-398704963dd4e38b.rmeta`|
```

The failure rate is pretty small (depends heavily on the hardware).