See alexcrichton/cargo-vendor#70

Would be nice to be able to vendor on linux without pulling in windows-specific dependencies.
This would still be something we would use.

Related issues:

• Don't require existence of dependencies not needed for the current --target #5896
• Allow specifying a set of supported target platforms in Cargo.toml #6179
• Resolve dependencies based on feasible target/target_os platform combinations #15563