gtk/gtkwindow.c: Fix build on non-X11
gtk/gtkwindow.c: Fix build on non-X11

There were some code added to this file that is meant for the X11 backend,
but they are being unconditionally built.  Add build-time checks for the
X11 backend for these to fix the build on non-X11 platforms.

chergert/gtk,msteinert/gtk,ahodesuka/gtk,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,Adamovskiy/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,grubersjoe/adwaita,chergert/gtk,msteinert/gtk,jadahl/gtk,Lyude/gtk-,ahodesuka/gtk,davidgumberg/gtk,Lyude/gtk-,Lyude/gtk-,alexlarsson/gtk,ahodesuka/gtk,ebassi/gtk,alexlarsson/gtk,ahodesuka/gtk,jadahl/gtk,jigpu/gtk,jigpu/gtk,Lyude/gtk-,Lyude/gtk-,davidgumberg/gtk,chergert/gtk,jadahl/gtk,Adamovskiy/gtk,jadahl/gtk,Adamovskiy/gtk,alexlarsson/gtk,jessevdk/gtk,ahodesuka/gtk,ahodesuka/gtk,grubersjoe/adwaita,Sidnioulz/SandboxGtk,ebassi/gtk,Sidnioulz/SandboxGtk,ahodesuka/gtk,ebassi/gtk,Adamovskiy/gtk,jigpu/gtk,jadahl/gtk,jessevdk/gtk,Sidnioulz/SandboxGtk,jigpu/gtk,jessevdk/gtk,ebassi/gtk,alexlarsson/gtk,Sidnioulz/SandboxGtk,jessevdk/gtk,alexlarsson/gtk,jadahl/gtk,davidgumberg/gtk,jessevdk/gtk,alexlarsson/gtk,jessevdk/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jigpu/gtk,msteinert/gtk,alexlarsson/gtk,chergert/gtk,grubersjoe/adwaita,chergert/gtk,alexlarsson/gtk,Adamovskiy/gtk,jadahl/gtk,Lyude/gtk-,Adamovskiy/gtk,grubersjoe/adwaita,msteinert/gtk,chergert/gtk,msteinert/gtk,jessevdk/gtk,Lyude/gtk-,Lyude/gtk-,Adamovskiy/gtk,ebassi/gtk,Sidnioulz/SandboxGtk,davidgumberg/gtk,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,grubersjoe/adwaita,Adamovskiy/gtk,chergert/gtk,jadahl/gtk,ahodesuka/gtk,ebassi/gtk,jigpu/gtk,msteinert/gtk,chergert/gtk