xdata_xcursor-themes: add dependency on host xapp_xcursorgen

As reported in bug #3331, xdata_xcursor_themes needs the xcursorgen
application installed on the host. This commit adds this dependency,
together with the needed host libraries required for xapp_cursorgen to
build properly.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>