Wire up testing to ./x.py test in rust-lang/rust

[bjorn3]

• [x] https://github.com/bjorn3/rustc_codegen_cranelift/issues/1272
• [x] Copy build_sysroot/ to download/ to avoid modifying the source directory (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1338)
• [x] Remove hyperfine dependency for regular testing (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1338)
• [x] https://github.com/bjorn3/rustc_codegen_cranelift/issues/1280 (https://github.com/bjorn3/rustc_codegen_cranelift/commit/caacef29e6ad63d6b588715e809e78286d29db3f)
• [ ] https://github.com/bjorn3/rustc_codegen_cranelift/issues/1282
• [x] Support offline builds using cargo fetch (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1339)
• [ ] Support vendoring external dependencies using cargo vendor (~~https://github.com/bjorn3/rustc_codegen_cranelift/pull/1342~~ will be done in x.py instead)
• [x] Disable abi-checker outside of cg_clif's CI. It writes to it's source dir and is rather slow. (7095783)
• [x] Drop testing of simple-raytracer. Just keep it for benchmarking, but don't download it in ./y.rs prepare. (3ba9b13490b88a902ae74056a86aeaab038a6a40)
• [x] Skip jit tests in rust's CI (134dc334857e453c50f8ea31b13cbda106204f20)
• [x] Support building with specified rustc and cargo rather than rustup managed one (#1374)
• [x] https://github.com/rust-lang/rust/pull/105977 (to fix cg_clif on newer nightlies, updated rustc in 6c58be8e518e311d9769c595adad4bd30e65aff6)
• [ ] Modify rustbuild (https://github.com/rust-lang/rust/pull/112701)

[jyn514]

Support building with specified rustc and cargo rather than rustup managed one

If you respect RUSTC and CARGO, I think bootstrap already sets those today :) I wouldn't expect you to need a new argument to y.rs or anything like that.

https://github.com/bjorn3/rustc_codegen_cranelift/issues/1282

cc https://rust-lang.zulipchat.com/#narrow/stream/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202023-01-05/near/319616098 - I think this is ok not to require for now :)

[bjorn3]

Opened https://github.com/rust-lang/rust/pull/112701

[bjorn3]

The no_sysroot and base_sysroot parts of cg_clif's test suite has been running on rust's CI now for almost a month. The extended_sysroot part is blocked on vendoring support of the things being tested.