Update Redox SA_ constants.

[4lDO2]

Description

Redox completely redesigned its signal handling code last summer, but this wasn't upstreamed to the libc crate, making crates like signal-hook segfault.

It would be appreciated if a 0.2 minor version could be released with these changes.

Closes: #4262

Sources

https://gitlab.redox-os.org/redox-os/relibc/-/blob/master/src/header/signal/redox.rs?ref_type=heads#L43-50

underlying diff

https://gitlab.redox-os.org/redox-os/relibc/-/merge_requests/480/diffs#d174caa1d6ee478ceffe421ab58c6f035a7e7285_72_39

Checklist

• No placeholder or unstable values like *LAST or *MAX are
  included
• Tested locally using https://gitlab.redox-os.org/redox-os/acid/-/blob/master/src/proc.rs?ref_type=heads#L649-667 with and without this patch, respectively

@rustbot label +stable-nominated

[rustbot]

r? @tgross35

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[tgross35]

Thanks for the change!