Document `cargo-clippy` feature
It is possible to use conditional compilation to prevent Clippy from evaluating certain code at all. Unfortunately, it was no longer documented anywhere. This adds a brief explanation of how to use the feature with conditional compilation, and mentions a few downsides.
Fixes#10220 — Ability to skip files or blocks entirely
changelog: none
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It is possible to use conditional compilation to prevent Clippy from
evaluating certain code. This adds a brief explanation of how to use the
feature with conditional compilation, and mentions that generally it’s
preferable to use something like `#[allow(clippy::all)]`.
Fixes#10220 — Ability to skip files or blocks entirely
