cp, mv: return error for symlinks on non-unix/non-windows platforms

Replace cfg(not(windows)) with cfg(unix) for the symlink_file call,
and add a fallback that returns an unsupported error on platforms like
WASI that lack symlink support.

src/uu/cp/src/cp.rs

@@ -1898,7 +1898,17 @@ fn symlink_file(
     dest: &Path,
     symlinked_files: &mut HashSet<FileInformation>,
 ) -> CopyResult<()> {
-    #[cfg(not(windows))]
+    #[cfg(target_os = "wasi")]
+    {
+        return Err(CpError::IoErrContext(
+            std::io::Error::new(std::io::ErrorKind::Unsupported, "symlinks not supported"),
+            translate!("cp-error-cannot-create-symlink",
+                       "dest" => get_filename(dest).unwrap_or("?").quote(),
+                       "source" => get_filename(source).unwrap_or("?").quote()),
+        )
+        .into());
+    }
+    #[cfg(not(any(windows, target_os = "wasi")))]
     {
         std::os::unix::fs::symlink(source, dest).map_err(|e| {
             CpError::IoErrContext(

src/uu/mv/src/mv.rs

@@ -821,6 +821,8 @@ fn rename_with_fallback(
         const EXDEV: i32 = windows_sys::Win32::Foundation::ERROR_NOT_SAME_DEVICE as _;
         #[cfg(unix)]
         const EXDEV: i32 = libc::EXDEV as _;
+        #[cfg(target_os = "wasi")]
+        const EXDEV: i32 = 18; // POSIX EXDEV value
 
         // We will only copy if:
         // 1. Files are on different devices (EXDEV error)
@@ -926,9 +928,8 @@ fn rename_symlink_fallback(from: &Path, to: &Path) -> io::Result<()> {
     }
 }
 
-#[cfg(not(any(windows, unix)))]
+#[cfg(target_os = "wasi")]
 fn rename_symlink_fallback(from: &Path, to: &Path) -> io::Result<()> {
-    let path_symlink_points_to = fs::read_link(from)?;
     Err(io::Error::new(
         io::ErrorKind::Other,
         translate!("mv-error-no-symlink-support"),