os: fix build error on plan9

https://go-review.googlesource.com/#/c/27580 added the test.
However the test use syscall.ELOOP which is not defined on plan9.
Move test code from "os_test.go" to "os_windows_test.go" to prevent
build error.

Change-Id: Ie7f05bfb9ab229e06a8e82a4b3b8a7ca82d4663b
Reviewed-on: https://go-review.googlesource.com/27833
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David du Colombier <0intro@gmail.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/os/os_test.go

@@ -1812,26 +1812,3 @@ func TestRemoveAllRace(t *testing.T) {
 	close(hold) // let workers race to remove root
 	wg.Wait()
 }
-
-func TestStatSymlinkLoop(t *testing.T) {
-	testenv.MustHaveSymlink(t)
-
-	defer chtmpdir(t)()
-
-	err := Symlink("x", "y")
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer Remove("y")
-
-	err = Symlink("y", "x")
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer Remove("x")
-
-	_, err = Stat("x")
-	if perr, ok := err.(*PathError); !ok || perr.Err != syscall.ELOOP {
-		t.Errorf("expected *PathError with ELOOP, got %T: %v\n", err, err)
-	}
-}

src/os/os_windows_test.go

@@ -5,6 +5,7 @@
 package os_test
 
 import (
+	"internal/testenv"
 	"io/ioutil"
 	"os"
 	osexec "os/exec"
@@ -229,3 +230,26 @@ func TestDeleteReadOnly(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestStatSymlinkLoop(t *testing.T) {
+	testenv.MustHaveSymlink(t)
+
+	defer chtmpdir(t)()
+
+	err := os.Symlink("x", "y")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove("y")
+
+	err = os.Symlink("y", "x")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove("x")
+
+	_, err = os.Stat("x")
+	if perr, ok := err.(*os.PathError); !ok || perr.Err != syscall.ELOOP {
+		t.Errorf("expected *PathError with ELOOP, got %T: %v\n", err, err)
+	}
+}