os: remove read-only directories in RemoveAll on Windows

Remove skipping of TestRemoveUnreadableDir on Windows.

Fixes #26295

Change-Id: I364a3caa55406c855ece807759f6298f7e4ddf1e
Reviewed-on: https://go-review.googlesource.com/c/go/+/203599
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/os/removeall_noat.go

@@ -8,6 +8,7 @@ package os
 
 import (
 	"io"
+	"runtime"
 	"syscall"
 )
 
@@ -127,6 +128,13 @@ func removeAll(path string) error {
 	if err1 == nil || IsNotExist(err1) {
 		return nil
 	}
+	if runtime.GOOS == "windows" && IsPermission(err1) {
+		if fs, err := Stat(path); err == nil {
+			if err = Chmod(path, FileMode(0200 | int(fs.Mode()))); err == nil {
+				err1 = Remove(path)
+			}
+		}
+	}
 	if err == nil {
 		err = err1
 	}

src/os/removeall_test.go

@@ -378,7 +378,7 @@ func TestRemoveAllButReadOnlyAndPathError(t *testing.T) {
 
 func TestRemoveUnreadableDir(t *testing.T) {
 	switch runtime.GOOS {
-	case "js", "windows":
+	case "js":
 		t.Skipf("skipping test on %s", runtime.GOOS)
 	}