Add SCHED_RESET_ON_FORK

[padenot]

This is a fix for #1511, and is valid for musl and glibc.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @gnzlbg (or someone else) soon.

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[gnzlbg]

@bors: r+

[bors]

📌 Commit 8299925 has been approved by gnzlbg

[bors]

⌛ Testing commit 8299925 with merge 9b936e3...

[bors]

☀️ Test successful - checks-cirrus-freebsd-11, checks-cirrus-freebsd-12, status-azure
Approved by: gnzlbg
Pushing 9b936e3 to master...