Auto merge of #143641 - Kobzol:tool-target, r=jieyouxu

Add `ToolTarget` to bootstrap

Oh, you thought I'm done with refactoring bootstrap tools? Na-ah, think again! After the failure of rust-lang/rust#143581, `ToolTarget` is back with a vengeance. This time, I implemented the test changes and tool cleanups without forcing these tools to be built with the stage0 compiler.

There are still some small wins though, `LlvmBitcodeLinker` now starts at stage 1, and not stage 2. Cargo should also be ported to this new mode, but I'm leaving that for a follow-up PR.

Hopefully X-th time's the charm 🤞

r? `@jieyouxu`

Author: bors