[rust-lang/rust] Any prrogram force-depends on sigaction (make std's signal handler optional)

### ROOT CAUSE The issue arises because the Rust standard library's signal handling relies on `sigaction`, which may not be available on all platforms. This causes the program to fail when `sigaction` is unavailable, unlike the C equivalent which handles this gracefully. ### CODE FIX To make the use of `sigaction` optional, modify the signal handling code to conditionally use it only if available. This can be achieved by using feature flags or runtime checks. Here's how to implement the fix: ```rust // Add a feature flag for sigaction #[cfg_attr(feature = "sigaction", feature(feature))] #[cfg_attr(feature = "sigaction", rust(feature))] #[cfg_attr(feature = "sigaction", feature)] #[cfg_attr(feature = "sigaction", rust)] #[cfg_attr(feature = "sigaction", feature)] #[cfg_attr(feature = "sigaction", rust)] // Modify the signal handling code #[cfg(feature = "sigaction")] pub unsafe fn set_handler(sig: libc::c_int, handler: libc::signal_t) { let old_handler; let res; { let handler = handler as *mut libc::signal_t; res = libc::sigaction(sig, &handler, &mut old_handler); } if res == libc::SIG_ERR { // Fallback to using signal() libc::signal(sig, handler); } } // Remove the unconditional call to sigaction in the signal handling setup // Replace with conditional calls based on availability ``` This fix introduces a feature flag to conditionally use `sigaction` and falls back to `signal()` if `sigaction` isn't available or fails, ensuring the program remains robust across different platforms.