ln: add WASI support via symlink_path

On wasm32-wasip1, std::os::unix::fs::symlink is not available, but
WASI preview 1 provides path_symlink which Rust exposes as
std::os::wasi::fs::symlink_path. Import it under the symlink alias
so the existing call site works without changes.

Follows the same pattern as cp.rs for enabling wasi_ext.

Author: DePasqualeOrg

src/uu/ln/src/ln.rs

@@ -3,6 +3,8 @@
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
 
+#![cfg_attr(target_os = "wasi", feature(wasi_ext))]
+
 // spell-checker:ignore (ToDO) srcpath targetpath EEXIST
 
 use clap::{Arg, ArgAction, Command};
@@ -21,6 +23,8 @@ use thiserror::Error;
 
 #[cfg(any(unix, target_os = "redox"))]
 use std::os::unix::fs::symlink;
+#[cfg(target_os = "wasi")]
+use std::os::wasi::fs::symlink_path as symlink;
 #[cfg(windows)]
 use std::os::windows::fs::{symlink_dir, symlink_file};
 use std::path::{Path, PathBuf};
@@ -488,11 +492,3 @@ pub fn symlink<P1: AsRef<Path>, P2: AsRef<Path>>(src: P1, dst: P2) -> std::io::R
         symlink_file(src, dst)
     }
 }
-
-#[cfg(target_os = "wasi")]
-fn symlink<P1: AsRef<Path>, P2: AsRef<Path>>(_src: P1, _dst: P2) -> std::io::Result<()> {
-    Err(std::io::Error::new(
-        std::io::ErrorKind::Unsupported,
-        "symlinks not supported on this platform",
-    ))
-}