automake2junit.ml: ignore symlinks when searching for .trs files

One gnulib test creates a symlink to the same directory, causing our
iteration to read the same test directory over and over, every time
considering it as new level of subdirectory.

As solution (or workaround), when iterating through a directory consider
only regular files, and directories, ignoring any other file type
(symlinks included).

tests/automake2junit.ml

@@ -19,6 +19,7 @@
 
 open Printf
 #load "str.cma"
+#load "unix.cma"
 
 type test_result =
   | Pass
@@ -80,14 +81,21 @@ let rec string_replace s s1 s2 =
   )
 
 let find_trs basedir =
+  let split_dirs_and_files items =
+    let rec work dirs files = function
+      | [] -> dirs, files
+      | ((_, full_x) as x) :: xs ->
+        match (Unix.lstat full_x).Unix.st_kind with
+        | Unix.S_REG -> work dirs (x :: files) xs
+        | Unix.S_DIR -> work (x :: dirs) files xs
+        | _ -> work dirs files xs
+    in
+    work [] [] items
+  in
   let rec internal_find_trs basedir stack =
     let items = Array.to_list (Sys.readdir basedir) in
     let items = List.map (fun x -> x, basedir // x) items in
-    let dirs, files = List.partition (
-      fun (_, full_x) ->
-        try Sys.is_directory full_x
-        with Sys_error _ -> false
-    ) items in
+    let dirs, files = split_dirs_and_files items in
     let files = List.filter (fun (x, _) -> Filename.check_suffix x ".trs") files in
     let files = List.map (fun (_, full_x) -> stack, full_x) files in
     let subdirs_files = List.fold_left (