Auto merge of #5151 - flip1995:fix_run_pass_tests, r=flip1995
Auto merge of #5151 - flip1995:fix_run_pass_tests, r=flip1995

Fix run-pass tests when CARGO_TARGET_DIR is not set

r? @lzutao

I got

```
thread '[ui] ui/crashes/ice-1969.rs' panicked at 'failed to exec `"target/debug/test_build_base/crashes/ice-1969.stage-id"`: Os { code: 2, kind: NotFound, message: "No such file or directory" }', /home/pkrones/.cargo/registry/src/github.com-1ecc6299db9ec823/compiletest_rs-0.4.0/src/runtest.rs:1350:25
```

on tests with `// run-pass` locally. The reason for this is, that I haven't set `CARGO_TARGET_DIR` and then `"target"` was used as the `CARGO_TARGET_DIR`. It seems, that `compiletest-rs` cannot deal with relative paths for `// run-pass` tests.

changelog: none

graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust