Add macos futex impl

Shamelessly stolen from pending PR: rust-lang/rust#122408

Author: Grimeh

Cargo.toml

@@ -6,10 +6,12 @@ keywords = ["atomic", "futex"]
 version = "1.1.0"
 edition = "2021"
 license = "BSD-2-Clause"
-categories = ["concurrency", "os", "no-std"]
+categories = ["concurrency", "os"]
 
-[target.'cfg(any(target_os = "linux", target_os = "android", target_os = "freebsd"))'.dependencies]
+[target.'cfg(any(target_os = "linux", target_os = "android", target_os = "freebsd", target_vendor = "apple"))'.dependencies]
 libc = "0.2"
+cfg-if = "1.0.0"
+memchr = "2.7.4"
 
 [target.'cfg(windows)'.dependencies]
 windows-sys = { version = "0.42.0", features = ["Win32_System_Threading", "Win32_Foundation", "Win32_System_WindowsProgramming"] }

src/lib.rs

@@ -1,8 +1,9 @@
-#![no_std]
 #![doc = include_str!("../README.md")]
 
 use core::sync::atomic::{AtomicPtr, AtomicU32, AtomicU64};
 
+mod unix_futex;
+
 #[cfg(any(target_os = "linux", target_os = "android"))]
 #[path = "linux.rs"]
 mod platform;