Rollup merge of #126318 - Kobzol:bootstrap-perf, r=onur-ozkan

Add a `x perf` command for integrating bootstrap with `rustc-perf`

This PR adds a new `x perf` command to bootstrap. The idea is to let rustc developers profile (`profile_local`) and benchmark (`bench_local`) a stage1/stage2 compiler directly from within `rust`.

Before, if you wanted to use `rustc-perf`, you had to clone it, set it up, copy the `rustc` sysroot after every change to `rust` etc. This is an attempt to automate that.

I opened this PR mostly for discussion. My idea is to offer an interface that looks something like this (a random sample of commands):
```bash
x perf --stage 2 profile eprintln
x perf --stage1 profile cachegrind
x perf benchmark --id baseline
x perf benchmark --id after-edit
x perf cmp baseline after-edit
```

In this PR, I'd like to only implement the simplest case (`profile_local (eprintln)`), because that only requires a single sysroot (you don't compare anything), and it's relatively easy to set up. Also, I'd like to avoid forcing developers to deal with the rustc-perf UI, so more complex use-cases (like benchmarking two sysroots and comparing the results) should probably wait for rust-lang/rustc-perf#1734 (which is hopefully coming along soon-ish).

I'm not sure if it's better to do this in bootstrap directly, or if I should create some shim tool that will receive a `rustc` sysroot, and offer a simplified CLI on top of `rustc-perf`.

## Why is a separate CLI needed?
We definitely need to add some support to bootstrap to automate preparing `rustc-perf` and the `rustc` sysroot, but in theory after that we could just let people invoke `rustc-perf` manually. While that is definitely possible, you'd need to manually figure out where is your sysroot located, which seems annoying to me. The `rustc-perf` CLI is also relatively complex, and for this use-case it makes sense to only use a subset of it. So I thought that it would be better to offer a simplified interface on top of it that would make life easier for contributors. But maybe it's not worth it.

CC `@onur-ozkan`

Author: matthiaskrgr