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!

[xtqqczze]

breaking change?

error[E0308]: mismatched types
   --> /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/nix-0.30.1/src/sys/signal.rs:809:22
    |
809 |                 _ => (flags - SaFlags::SA_SIGINFO).bits(),
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `i32`, found `u64`
    |
help: you can convert a `u64` to an `i32` and panic if the converted value doesn't fit
    |
809 |                 _ => (flags - SaFlags::SA_SIGINFO).bits().try_into().unwrap(),
    |                                                          ++++++++++++++++++++

Issue opened downstream: nix-rust/nix#2750

[xtqqczze]

Need to fix the types for the constants, e.g. SA_SIGINFO: c_int: opened #5009