message: Add rustc-workspace-hack.
diff: @@ -39,6 +39,10 @@ directories = { version = "1.0", optional = true }
  rustc_version = { version = "0.2.3", optional = true }
  env_logger = "0.5"
  log = "0.4"
  +# A noop dependency that changes in the Rust repository, it's a bit of a hack.
  +# See the `src/tools/rustc-workspace-hack/README.md` file in `rust-lang/rust`
  +# for more information.
  +rustc-workspace-hack = "1.0.0"
  [build-dependencies]
  vergen = "3"
  