rustc-dev component does not work

[RalfJung]

After doing rustup-toolchain-install-master -c rust-src -c rustc-dev and setting that toolchain as a local override, cargo build in https://github.com/rust-lang/miri/ should work. However, it does not:

error[E0463]: can't find crate for `syntax`
 --> src/lib.rs:9:1
  |
9 | extern crate syntax;
  | ^^^^^^^^^^^^^^^^^^^^ can't find crate

error: aborting due to previous error

According to rust-lang/rust#64823 (comment), extracting the tarball manually works fine, so this looks like an issue with this tool.

Might be a duplicate of #15.

This bug currently halts Miri and Clippy development.