Fix check-cfg-related and rust-lld-related CI failures

[ryoqun]

Fix master ci, which is broken due 2 problems:

• the new check-cfg: https://blog.rust-lang.org/2024/05/06/check-cfg.html
• the default linker change: https://blog.rust-lang.org/2024/05/17/enabling-rust-lld-on-linux.html

[ryoqun]

seems this warn isn't avoidable, when locally-developing crossbeam itself with any toolchain with the support of Cargo.toml's lints.rust and < nightly-2024-05-19..:

$ RUSTUP_TOOLCHAIN=1.78.0-x86_64-unknown-linux-gnu cargo check
warning: /home/ryoqun/work/crossbeam/Cargo.toml: unused manifest key: workspace.lints.rust.unexpected_cfgs.check-cfg
   Compiling crossbeam-utils v0.8.19 (/home/ryoqun/work/crossbeam/crossbeam-utils)

[Urgau]

Btw, we are working on making this warning go away in the current beta with rust-lang/cargo#13925, so that when it reaches stable, the warning would already be gone by the previous version.

[ryoqun]

@github-actions CI / careful (pull_request) Failing after 42s

well, well, well. celebrate rapid development progress of rust nightly? seems https://blog.rust-lang.org/2024/05/17/enabling-rust-lld-on-linux.html is the culprit for the careful failure...

[ryoqun]

@taiki-e Following from #1109 (comment), it seems ci is green again in another approach. could you review this?

[taiki-e]

Thanks!