There is a new pull request by zdykstra against master on the void-packages repository

https://github.com/zdykstra/void-packages xdm
https://github.com/void-linux/void-packages/pull/21255

xdm: add more conf_files
When configuring XDM for remote access, a number of the files in /etc/X11/xdm need to be modified to enable this support. Package upgrades should not overwrite changes to these files.

A patch file from https://github.com/void-linux/void-packages/pull/21255.patch is attached