Publish compiletest as a rustc-tools component

[Mark-Simulacrum]

The goal of this PR is to just get the publishing working in a way that'll hopefully let clippy consume the resulting binary without too much trouble. If there's a desire to use compiletest as a library rather than a binary, I see no reason why we couldn't publish an rlib/.so/whatever, just like we do for std or the rustc libraries, that'll just take more plumbing. My hope is that the binary is a sufficient interface for now, since that works for rustc itself (bootstrap calls the binary), but if not, we can modify this PR to publish an rlib into the sysroot too, when the compiletest component is installed.

It looks like as-is clippy does use the library compiletest-rs as a library for its testing, I would need to do more digging to tell if that's an intrinsic dependency or not.

cc @Manishearth @oli-obk rust-lang/compiler-team#536

r? @jyn514

[Mark-Simulacrum]

@bors try

[bors]

⌛ Trying commit 6d7529751460ac93bcdf0b62122bc299e0d24060 with merge 9834b0310d8ad7a4fbca6ee673ffea9161757275...

[jyn514]

I think we should hold off on merging this until we confirm with the clippy team this is the approach they want to take. No objection to doing this, just don't want it to be wasted work.

[Mark-Simulacrum]

Sure, that's fine with me -- in particular clarity on library vs. binary I think would be good.

Mostly wanted to open this so we can get a try build + a "fake" nightly published from it so it's easier to experiment with (for example) a clippy PR migrating to this.

[bors]

☀️ Try build successful - checks-actions
Build commit: 9834b0310d8ad7a4fbca6ee673ffea9161757275 (9834b0310d8ad7a4fbca6ee673ffea9161757275)

[Mark-Simulacrum]

@bors try

[bors]

⌛ Trying commit 9223b0c with merge 1a32bcf2c3a5c2b33a30b93b1228eb9eb7ca6a9f...

[Manishearth]

cc @rust-lang/clippy

[bors]

☀️ Try build successful - checks-actions
Build commit: 1a32bcf2c3a5c2b33a30b93b1228eb9eb7ca6a9f (1a32bcf2c3a5c2b33a30b93b1228eb9eb7ca6a9f)