fix(collector): allow unused imports in serde-1.0.136

[bvanjoi]

cc @Kobzol

[Kobzol]

It's possible that there are also some other benchmarks that fail, as we have only tried the "training crates" on CI, but since the build didn't succeed, the full benchmark run didn't finish.

If you have a build of the compiler with the corresponding change from the PR, could you please try to run the whole compilation benchmark suite locally, to see if it works?

$ cargo build
$ cargo run --bin collector bench_local <path-to-rustc> --self-profile

We should make sure that it works, because after we update rustc-perf, we also need to send another PR to rust-lang/rust, to update to the modified rustc-perf suite for PGO/BOLT training.

[bvanjoi]

could you please try to run the whole compilation benchmark suite locally, to see if it works

I sequentially ran cargo +stage1 build for each project within compile-benchmarks and runtime-benchmarks, and found that the unused_imports error occurred exclusively in serde.

• (stage1 is build on report unused_import for empty reexports even it is pub rust#116033)
• (The reason I refrained from using cargo run --bin collector xxx is due to my local environment being macos, which doesn't support pref.)

But there has another errors:

• build compile-benchmarks/stm32f4-0.14.0 failed with:

error[E0460]: found possibly newer version of crate `std` which `rustc_version` depends on
 --> bare-metal-0.2.5/build.rs:1:1
  |
1 | extern crate rustc_version;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: perhaps that crate needs to be recompiled?
  = note: the following crate versions were found:
// ....
Some errors have detailed explanations: E0432, E0460, E0463.
For more information about an error, try `rustc --explain E0432`.
error: could not compile `syn` (lib) due to 5 previous errors

• build compile-benchmarks/style-servo failed with:

error[E0460]: found possibly newer version of crate `std` which `app_units` depends on
  --> components/style_traits/lib.rs:16:1
   |
16 | extern crate app_units;

// .....
For more information about this error, try `rustc --explain E0503`.
error: could not compile `getopts` (lib) due to previous error

• build compile-benchmarks/tokio-webpush-simple failed with:

error[E0460]: found possibly newer version of crate `std` which `tokio_core` depends on
// .....
For more information about this error, try `rustc --explain E0460`.
error: could not compile `serde_json` (lib) due to 15 previous errors
error: could not compile `tokio-proto` (lib) due to 100 previous errors

• build compile-benchmarks/webrender-2022 failed with:

// ....
error: cannot determine resolution for the derive macro `PeekPoke
// ....
Some errors have detailed explanations: E0412, E0432, E0433, E0460, E0463.
For more information about an error, try `rustc --explain E0412`.
error: could not compile `webrender_api` (lib) due to 449 previous errors

• build runtime-benchmarks/svg failed with:

// .....
error[E0282]: type annotations needed
// .....
Some errors have detailed explanations: E0282, E0460, E0463, E0599.
For more information about an error, try `rustc --explain E0282`.
error: could not compile `resvg` (lib) due to 642 previous errors

I'm uncertain if this error aligns with the expected outcome, but it appears unrelated to rust-lang/rust#116033.

[Kobzol]

Yes that appears to be flaky, possibly some OS X thing. Thanks! I will create a PR on rust-lang/rust to sync rustc-perf.