libdispatch was first released with Mac OS X 10.6.
See https://en.wikipedia.org/wiki/Grand_Central_Dispatch
See https://github.com/rust-lang/rust/commit/99182dd8058f0a1153b8b7fcf873028caa6fbfa7

--- library/std/src/sys/pal/unix/thread_parking/mod.rs.orig	2022-12-12 09:02:12.000000000 -0700
+++ library/std/src/sys/pal/unix/thread_parking/mod.rs	2022-12-26 20:54:40.000000000 -0700
@@ -20,8 +20,8 @@
         ),
         not(miri),
     ))] {
-        mod darwin;
-        pub use darwin::Parker;
+        mod pthread;
+        pub use pthread::Parker;
     } else if #[cfg(target_os = "netbsd")] {
         mod netbsd;
         pub use netbsd::{current, park, park_timeout, unpark, ThreadId};