Remove rlibs as final artifacts

[epage]

Only treat rlibs as intermediate artifacts and not final artifacts, meaning that they would only be found in build-dir and not also the target-dir at paths like target/release/foo.rlib.

The problem with rlibs is that Cargo does not uplift any rlib dependencies to being final artifacts as well. This makes it so the only ways to successfully use rlibs are

• have no dependencies so when you build, all rlibs you care about are uplifted
• only use build-dir rlibs by monitoring json messages from cargo

As this seems broken, this should be fine within our compatibility guarantees to change but I am wondering if there is anything I am overlooking

By making this change, it reduces the conversations we have to have around what are safe evolutions of rlibs, e.g. #15495

[epage]

The scream test at #17267 will help identify problems with this idea

I've also posted to

• #t-cargo/build-integration > Any users of rlibs as a final build artifact? @ 💬
• #t-compiler > Anyone know of people using rlibs generated by `cargo build` @ 💬
• https://hachyderm.io/@epage/116999642073706513

So far, the only concerns raised

• Bootstrap needing to possible update
• Confirm what is in the json messages
  • Are dep rlibs included?
  • Are local rlibs shown using intermediate or final path? What would it take to change this?