Some headers making use of X_EXPORT macro, so Xfuncproto.h should be
included explicitly, instead of silently relying any other include
already doing that.
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1813>