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

https://github.com/marmeladema/void-packages mesa-21.0
https://github.com/void-linux/void-packages/pull/29520

mesa: update to 21.0.0
Friendly take over / continuation of https://github.com/void-linux/void-packages/pull/27956

A patch file from https://github.com/void-linux/void-packages/pull/29520.patch is attached