Add support for building rustc-perf and running the collector on Windows

[wesleywiser]

This PR implements the first two parts of #834: basic support for building the code on Windows and support for profiling using -Zself-profile.

Currently, running all tests works, other than a number of benchmarks that fail to build on my machine due to missing native dependencies (such as webrender).

The general strategy I took was to rewrite in Rust whenever convenient, otherwise falling back to a Windows equivalent of the unix-y tool.

Part of #834

[Mark-Simulacrum]

It looks like CI is failing non-spuriously here - it'll currently fail even on master due to syn incremental being broken in rustc itself, though, so you won't get it fully green :)

Before we land this we should likely add a windows builder to CI to make sure we don't accidentally break support; at least just basic building (e.g. cargo check), but maybe something more involved would work too. I don't think we can use perf stat on Windows, so perhaps a self-profile collection on a few benchmarks would also help iron out any latent bugs.

Otherwise I think this approach looks really good to me - some duplication and expansion for sure, but nothing too surprising or unacceptable I think :) Thanks!

[rylev]

This would break if any subfolder is named target no?

[Mark-Simulacrum]

I think that's only true if the subfolder actually needs touching; I'm not sure that will happen in practice. Realistically we can likely get away with touching the crate "roots" only, but those are a bit annoying to identify.

[Mark-Simulacrum]

Hey @wesleywiser -- I noticed this is still marked as [WIP] but wondering if that's no longer actually the case?

[Mark-Simulacrum]

2021-05-18T20:26:27.1254410Z [2021-05-18T20:26:27Z DEBUG collector::execute] applying patch add static arr item
2021-05-18T20:26:27.1255811Z [2021-05-18T20:26:27Z DEBUG collector::execute] applying add static arr item to "/tmp/.tmpV933YN"
2021-05-18T20:26:27.1330858Z error: patch failed: src/main.rs:65572
2021-05-18T20:26:27.1331599Z error: src/main.rs: patch does not apply
2021-05-18T20:26:27.1344711Z collector error: Failed to benchmark 'coercions', recorded: expected success, got exit status: 1

[wesleywiser]

I believe this is ready for a final review. I've updated the title and description of the PR to match the current state and I've tested running a basic profile_local command on both Windows & Linux with success.

[rylev]

🎉