gdk: Ignore clipboard_get()'s deprecation warnings
gdk: Ignore clipboard_get()'s deprecation warnings

Its implementation is modeled after gtk_dialog_run() which still uses
these deprecated thread functions.

Signed-off-by: Francois Gouget <6b915da68578f6eb004fe99432b967565fc9be8f@codeweavers.com>
Acked-by: Jonathon Jongsma <c7254805a17bd5c41e24c3a278fcbf3afcdfb0fa@redhat.com>

flexVDI/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk