change sa_flags in sigaction to c_int on redox

[auronandace]

Description

Changes sa_flags in sigaction to c_int for redox as per POSIX specification.

Sources

sa_flags in sigaction the rust signal header: https://gitlab.redox-os.org/redox-os/relibc/-/blob/ee6a6062cd6c6b57e7617559d988895d8a73ec64/src/header/signal/mod.rs#L56

sa_flags in sigaction in the C include file: https://gitlab.redox-os.org/redox-os/relibc/-/blob/28ffabebf629172a6c0c00ca56f73d72f25f7c6e/include/bits/signal.h#L19

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

@rustbot label +stable-nominated

[JohnTitor]

Thanks!