[tracking] can't use global workspace-hack crate because of bugs in cargo

[sunshowers]

cargo hakari 0.9.9 used a scheme where it would assume everything could target the same workspace-hack crate. Unfortunately, it turns out that cargo has a few bugs which prevent that from working:

Running cargo build -p workspace-hack -p <crate that depends on external workspace-hack> results in:

error: There are multiple `workspace-hack` packages in your project, and the specification `workspace-hack` is ambiguous.
Please re-run this command with `-p <spec>` where `<spec>` is one of the following:
  file:///opt/git/diem/crates/workspace-hack#0.1.0
  https://github.com/rust-lang/crates.io-index#workspace-hack:0.1.0

Also, if there's a local workspace-hack, trying to add a path dependency that also has a local workspace-hack can cause Cargo to produce a conflict error while writing out Cargo.lock.