Support running cargo rustc #823
Description
The motivation is that we want to test changes on all leaf crates without the building terminated by intermediate dependency failure.
Currently regressed dependencies prevent us from knowing whether their dependents regress or not.
cargo rustc will allow us to pass rustflags to the leaf crates only.
I'd be happy to help implement it if you favor the idea. It would probably be similar to the cargo doc one.
Updated: Found a walkaround. We can manually check whether tcx.sess.opts.lint_cap==allow to determine whether this crate is a dependency. Cargo automatically passes --cap-lints allow to dependencies.