There is an updated pull request by Duncaen against master on the void-packages repository

https://github.com/Duncaen/void-packages 32bit
https://github.com/void-linux/void-packages/pull/14822

xbps-src: add back support for 32bit dependencies
This will use xbps-query to see if packages that don't have a template file already exist and allows building packages like `gcc-multilib` again.
If the package doesn't exist already it will just error out, because `xbps-src` can't switch to a 32bit masterdir to build it. 

A patch file from https://github.com/void-linux/void-packages/pull/14822.patch is attached