Add rustc-dev component option

[elichai]

Fixes #100
I added a --with-dev option to download rustc-dev.
Because of rust-lang/rust#72594 I also install llvm-tools together with rustc-dev

[ehuss]

Maybe it would be more flexible to add a --component flag similar to rustup-toolchain-install-master so that you can specify any component?

[Mark-Simulacrum]

Yeah I think that would probably be the way to go, and we can still do some auto-detection for installing llvm-tools-preview.

It might also be good to consider dropping our custom installation code in favor of forking out to rustup-toolchain-install-master, and documenting that as a pre-req for bisection. (Maybe we can get a library version of it published, too).

[spastorino]

What is the status of this? cc @elichai

[elichai]

@spastorino not sure what's the next step, can it be merged as is? or do we want the --component flag? or maybe depend on rustup-toolchain-install-master somehow?

[spastorino]

Maybe @ehuss or @Mark-Simulacrum can clarify a bit and guide you better than I

[Mark-Simulacrum]

I think we should probably just merge. While I continue to think that a general component flag is the way to go, this is still likely a useful step. Ultimately I do think it makes sense for us to find a way to avoid a bunch of tools repeating the rustup-toolchain-install-master-like logic to install a set of rustup components for a particular commit; perhaps that means rustup-toolchain-install-master should become a library instead of just a cargo-install command, not sure.