rmdir: match GNU error output

Related to #2258

src/uu/rmdir/src/rmdir.rs

@@ -20,6 +20,11 @@ static OPT_VERBOSE: &str = "verbose";
 
 static ARG_DIRS: &str = "dirs";
 
+#[cfg(unix)]
+static ENOTDIR: i32 = 20;
+#[cfg(windows)]
+static ENOTDIR: i32 = 267;
+
 fn get_usage() -> String {
     format!("{0} [OPTION]... DIRECTORY...", executable!())
 }
@@ -105,6 +110,10 @@ fn remove(dirs: Vec<String>, ignore: bool, parents: bool, verbose: bool) -> Resu
 fn remove_dir(path: &Path, ignore: bool, verbose: bool) -> Result<(), i32> {
     let mut read_dir = match fs::read_dir(path) {
         Ok(m) => m,
+        Err(e) if e.raw_os_error() == Some(ENOTDIR) => {
+            show_error!("failed to remove '{}': Not a directory", path.display());
+            return Err(1);
+        }
         Err(e) => {
             show_error!("reading directory '{}': {}", path.display(), e);
             return Err(1);

tests/by-util/test_rmdir.rs

@@ -108,3 +108,19 @@ fn test_rmdir_ignore_nonempty_directory_with_parents() {
 
     assert!(at.dir_exists(dir));
 }
+
+#[test]
+fn test_rmdir_remove_symlink_match_gnu_error() {
+    let (at, mut ucmd) = at_and_ucmd!();
+
+    let file = "file";
+    let fl = "fl";
+    at.touch(file);
+    assert!(at.file_exists(file));
+    at.symlink_file(file, fl);
+    assert!(at.file_exists(fl));
+
+    ucmd.arg("fl/")
+        .fails()
+        .stderr_is("rmdir: failed to remove 'fl/': Not a directory");
+}