dix-config.h always needs to be included first, otherwise things
can get messed up in really obscure ways, eg. certain types silently
changing in size and causing mysterious crashes.
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1813>