[experiment] expand: Make #[derive(A, B, ...)] cfg-eval its input only for A, B, ...

[petrochenkov]

The second item from #83824 (comment).

[rust-highfive]

r? @matthewjasper

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[petrochenkov]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit e45d869 with merge f980a6509ca6ba43d60fdc29723f7b3c7b8497f1...

[bors]

☀️ Try build successful - checks-actions
Build commit: f980a6509ca6ba43d60fdc29723f7b3c7b8497f1 (f980a6509ca6ba43d60fdc29723f7b3c7b8497f1)

[rust-timer]

Queued f980a6509ca6ba43d60fdc29723f7b3c7b8497f1 with parent 3740ba2, future comparison URL.

[rust-timer]

Finished benchmarking try commit (f980a6509ca6ba43d60fdc29723f7b3c7b8497f1): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf

[petrochenkov]

Not a regression.