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

https://github.com/ericonr/void-packages spdlog
https://github.com/void-linux/void-packages/pull/26363

spdlog: use external libfmt.
@Johnnynator 

A patch file from https://github.com/void-linux/void-packages/pull/26363.patch is attached