Add fdatasync for missing platforms

CHANGELOG.md

@@ -9,6 +9,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - Added fine-grained features flags.  Most Nix functionality can now be
   conditionally enabled.  By default, all features are enabled.
   (#[1611](https://github.com/nix-rust/nix/pull/1611))
+- Added `fdatasync` for FreeBSD, Fuchsia, NetBSD, and OpenBSD.
+  (#[1581](https://github.com/nix-rust/nix/pull/1581))
 
 ### Changed
 ### Fixed

src/unistd.rs

@@ -1325,11 +1325,13 @@ pub fn fsync(fd: RawFd) -> Result<()> {
 ///
 /// See also
 /// [fdatasync(2)](https://pubs.opengroup.org/onlinepubs/9699919799/functions/fdatasync.html)
-// `fdatasync(2) is in POSIX, but in libc it is only defined in `libc::notbsd`.
-// TODO: exclude only Apple systems after https://github.com/rust-lang/libc/pull/211
 #[cfg(any(target_os = "linux",
           target_os = "android",
           target_os = "emscripten",
+          target_os = "freebsd",
+          target_os = "fuchsia",
+          target_os = "netbsd",
+          target_os = "openbsd",
           target_os = "illumos",
           target_os = "solaris"))]
 #[inline]