macos: add signal shim for downstream rust-vmm crates

.gitignore

@@ -3,3 +3,4 @@
 **/*.rs.bk
 Cargo.lock
 
+.DS_Store

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Added
 
 - [[#254](https://github.com/rust-vmm/vmm-sys-util/pull/254)]: Support `TFD_NONBLOCK` for `timerfd::TimerFd`.
+- [[#268](https://github.com/rust-vmm/vmm-sys-util/pull/268)]: Add macOS support for the `signal` module. The shim is gated behind `#[cfg(target_os = "macos")]` and adds no new dependencies; Linux and Android builds are unaffected. macOS consumers needing epoll-shaped polling should use `mio` (see vhost #316). `eventfd` is not provided: the cross-platform `EventConsumer`/`EventNotifier` primitive added in #244 already covers the daemon use case, and `vhost`'s public traits that take `&EventFd` are Linux-only callers (a follow-up gates them on Linux).
 
 ## v0.15.0
 

src/lib.rs

@@ -12,6 +12,11 @@ mod linux;
 #[cfg(any(target_os = "linux", target_os = "android"))]
 pub use crate::linux::*;
 
+#[cfg(target_os = "macos")]
+mod macos;
+#[cfg(target_os = "macos")]
+pub use crate::macos::*;
+
 #[cfg(unix)]
 mod unix;
 #[cfg(unix)]

src/macos/mod.rs

@@ -0,0 +1,6 @@
+// Copyright 2024 rust-vmm Authors. All Rights Reserved.
+// SPDX-License-Identifier: BSD-3-Clause
+
+//! macOS-specific modules providing compatibility shims for Linux-only APIs.
+
+pub mod signal;