Enable deny(unused_crate_dependencies) in all compiler/ crates.

[nnethercote]

And remove a couple of unused dependencies that this found.

r? @jackh726

[rustbot]

Some changes occurred in exhaustiveness checking

cc @Nadrieril

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

This PR changes Stable MIR

cc @oli-obk, @celinval, @ouz-a

Some changes occurred in diagnostic error codes

cc @GuillaumeGomez

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in compiler/rustc_sanitizers

cc @rust-lang/project-exploit-mitigations, @rcvalle

[nnethercote]

The false positives mentioned in the FIXME comments are annoying. I started a Zulip thread to ask about that.

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    Checking getrandom v0.2.15
    Checking rustc_data_structures v0.0.0 (/checkout/compiler/rustc_data_structures)
    Checking rand_core v0.6.4
   Compiling thiserror v1.0.61
error: external crate `libc` unused in `rustc_data_structures`: remove the dependency or add `use libc as _;`
note: the lint level is defined here
  --> compiler/rustc_data_structures/src/lib.rs:15:9
   |
15 | #![deny(unused_crate_dependencies)]

[nnethercote]

error: external crate `libc` unused in `rustc_data_structures`: remove the dependency or add `use libc as _;`

This error is because libc is used in rustc_data_structures for some platforms (Unix) but not for others (Windows). One way to fix would be to change the Cargo.toml file to list libc as a conditional dependency. The other way would be to add a use libc as _ to the lib.rs file. Not sure which is better. I'm feeling quite ambivalent about this PR overall.

[ChrisDenton]

One way to fix would be to change the Cargo.toml file to list libc as a conditional dependency. The other way would be to add a use libc as _ to the lib.rs file. Not sure which is better.

On the one hand I do prefer the former but on the other hand I don't really care that much...

[erikdesjardins]

I believe libc usage being removed on Windows was a deliberate change (cc @saethlin), so I'd suggest making it a conditional dependency so no future usages get added.

[saethlin]

Heh yes I wrote the PR to remove libc on Windows but the idea/motivation was @ChrisDenton.

[bors]

☔ The latest upstream changes (presumably #126319) made this pull request unmergeable. Please resolve the merge conflicts.

[jackh726]

Not sure if this needs a compiler MCP, at the very least, might be worth a team ping.

[nnethercote]

Based on the discussion in Zulip I think this lint isn't quite reliable enough to be used en masse like this. Which is a shame. I've filed #126368 for removing a couple more unused dependencies.