Auto merge of #4763 - michaelfairley:master, r=alexcrichton

Allow metadata hash to be computed when checking dylibs

Currently, `cargo check` on a dylib crate will use the same fingerprint files as `build`, resulting in `build`s often having to re-do unnecessary work as previous `build`s fingerprints have been clobbered (specifically, the `profile` hash in the fingerprint will be wrong since `check` runs with a different profile than `build`).