Consider stopping use of `extra_traits` feature due to soundness issues?

[erickt]

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There are apparently some soundness issues with libc's extra_traits feature in https://github.com/rust-lang/libc/issues/2700, https://github.com/rust-lang/libc/issues/2064, and https://github.com/rust-lang/libc/issues/2816, with an effort to remove the extra_traits feature to avoid this issue in https://github.com/rust-lang/libc/pull/3692. Would it be worthwhile removing it?