deps: gate selinux-related dependency set behind feat_selinux

[xtqqczze]

Follow-up #10360

The purpose of this change is to avoid pulling in Linux-specific dependencies such as selinux-sys when feat_selinux is not enabled, addressing the following TODO:

coreutils/src/uu/chcon/Cargo.toml

Line 22 in 157bbab

# TODO: block fetching crates without feat_selinux

[codspeed-hq]

Merging this PR will not alter performance

✅ 319 untouched benchmarks
⏩ 46 skipped benchmarks¹

---

_{Comparing xtqqczze:features-feat_selinux (a41da3b) with main (bd908f0)}

Footnotes

1. 46 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/tail-n0f (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/cut/cut-huge-range is now passing!

[xtqqczze]

@cakebaker @oech3 This doesn't seem to be correct approach in build.rs, any ideas?

[oech3]

I don't think cargo itself has solution satisfying everyone's requirements.

Someone might hope to see error with invalid combination of features (e.g, feat_selinux on macOS).

[xtqqczze]

#[cfg(...)] attributes are evaluated at compile time, but build.rs is compiled for and executed on the host machine, not the final target...