Switch strategies for how rustc's workspace is unioned

See rust-lang/rust#52919 for more details.

Cargo.toml

@@ -45,46 +45,6 @@ clippy_lints = { version = "0.0.212", path = "clippy_lints" }
 regex = "1"
 semver = "0.9"
 
-# Not actually needed right now but required to make sure that clippy/ and cargo build
-# with the same set of features in rust-lang/rust
-num-traits = "0.2" # enable the default feature
-backtrace = "0.3"
-
-# keep in sync with `cargo`'s `Cargo.toml'
-[target.'cfg(windows)'.dependencies.winapi]
-version = "0.3"
-features = [
-  # keep in sync with `cargo`'s `Cargo.toml'
-  "handleapi",
-  "jobapi",
-  "jobapi2",
-  "minwindef",
-  "ntdef",
-  "ntstatus",
-  "processenv",
-  "processthreadsapi",
-  "psapi",
-  "synchapi",
-  "winerror",
-  "winbase",
-  "wincon",
-  "winnt",
-  # no idea where these come from
-  "basetsd",
-  "lmcons",
-  "memoryapi",
-  "minschannel",
-  "minwinbase",
-  "ntsecapi",
-  "profileapi",
-  "schannel",
-  "securitybaseapi",
-  "synchapi",
-  "sysinfoapi",
-  "timezoneapi",
-  "wincrypt",
-]
-
 [dev-dependencies]
 cargo_metadata = "0.5"
 compiletest_rs = "0.3.7"
@@ -94,6 +54,11 @@ clippy-mini-macro-test = { version = "0.2", path = "mini-macro" }
 serde = "1.0"
 derive-new = "0.5"
 
+# 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]
 rustc_version = "0.2.2"
 ansi_term = "0.11"