enable xdg for next crosswalk rebase

I see that it xdg-shell is building again :

https://github.com/yejingfu/crosswalk/commit/1559b1a49c58e5280746c3e52831aea9cd1d177f

But this is not enough ... those 2 commits will be needed to enable xdg for next crosswalk rebase

Note this changeset is untested now , I just PR it to let you know

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