os: include 0111 in directory file mode on windows

Fixes #4444.

R=golang-dev, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/6858079

src/pkg/os/os_test.go

@@ -1095,3 +1095,15 @@ func TestLargeWriteToConsole(t *testing.T) {
 		t.Errorf("Write to os.Stderr should return %d; got %d", len(b), n)
 	}
 }
+
+func TestStatDirModeExec(t *testing.T) {
+	const mode = 0111
+	const path = "."
+	dir, err := Stat(path)
+	if err != nil {
+		t.Fatalf("Stat %q (looking for mode %#o): %s", path, mode, err)
+	}
+	if dir.Mode()&mode != mode {
+		t.Errorf("Stat %q: mode %#o want %#o", path, dir.Mode(), mode)
+	}
+}

src/pkg/os/stat_windows.go

@@ -190,7 +190,7 @@ func mkModTime(mtime syscall.Filetime) time.Time {
 
 func mkMode(fa uint32) (m FileMode) {
 	if fa&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
-		m |= ModeDir
+		m |= ModeDir | 0111
 	}
 	if fa&syscall.FILE_ATTRIBUTE_READONLY != 0 {
 		m |= 0444