/usr/include/xfce4/ is in libxfce4util-dev 4.12.1-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/xfce4/libxfce4util/
/usr/include/xfce4/libxfce4util/libxfce4util-config.h
/usr/include/xfce4/libxfce4util/libxfce4util.h
/usr/include/xfce4/libxfce4util/xfce-debug.h
/usr/include/xfce4/libxfce4util/xfce-fileutils.h
/usr/include/xfce4/libxfce4util/xfce-generics.h
/usr/include/xfce4/libxfce4util/xfce-i18n.h
/usr/include/xfce4/libxfce4util/xfce-kiosk.h
/usr/include/xfce4/libxfce4util/xfce-license.h
/usr/include/xfce4/libxfce4util/xfce-miscutils.h
/usr/include/xfce4/libxfce4util/xfce-posix-signal-handler.h
/usr/include/xfce4/libxfce4util/xfce-rc.h
/usr/include/xfce4/libxfce4util/xfce-resource.h
/usr/include/xfce4/libxfce4util/xfce-utf8.h