Cargo `build-dir` support

[epage]

The Cargo team has started a Call for Testing for build-dir which allows users to move intermediate artifacts out of their target-dir. This may break affect the behavior of cargo llvm-cov and I would recommend testing this feature out to identify if it does so you can prepare for when your users start using it (or for the future possibilities below), including

• Preparing any new workarounds.

Note:

• build-dir files do not have compatibility guarantees
• In the future we may change the default build-dir
• In the future, we may change the layout of build-dir

See rust-lang/cargo#14125 (comment)