Rollup merge of #111561 - dtolnay:compiletestdirexists, r=Mark-Simulacrum

Include better context for "already exists" error in compiletest

I encountered the following error from `x.py test tests/ui` today.

```console
---- [ui] tests/ui/impl-trait/multiple-lifetimes/multiple-lifetimes.rs stdout ----
thread '[ui] tests/ui/impl-trait/multiple-lifetimes/multiple-lifetimes.rs' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 17, kind: AlreadyExists, message: "File exists" }', src/tools/compiletest/src/runtest.rs:134:43
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

I found it impossible to unblock myself without knowing which directory it was stuck on.

Error message after this PR:

```console
---- [ui] tests/ui/impl-trait/multiple-lifetimes/multiple-lifetimes.rs stdout ----
thread '[ui] tests/ui/impl-trait/multiple-lifetimes/multiple-lifetimes.rs' panicked at 'called `Result::unwrap()` on an `Err` value: failed to create output base directory /git/rust/build/x86_64-unknown-linux-gnu/test/ui/impl-trait/multiple-lifetimes/multiple-lifetimes

Caused by:
    File exists (os error 17)', src/tools/compiletest/src/runtest.rs:139:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```

Now I was able to run `rm build/x86_64-unknown-linux-gnu/test/ui/impl-trait/multiple-lifetimes/multiple-lifetimes` and unblock myself.

Seems to be related to #109509 moving *tests/ui/impl-trait/multiple-lifetimes.rs* to *tests/ui/impl-trait/multiple-lifetimes/multiple-lifetimes.rs*.

0 files changed, 0 insertions, 0 deletions