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

https://github.com/ahesford/void-packages zfs
https://github.com/void-linux/void-packages/pull/20506

zfs: support building against linux5.6
This revision backports a patch to ZFS 0.8.3 to support building on Linux 5.6, which introduced some new interfaces used by the module and removed some deprecated functions.

Rather than wait for upstream to push out another release (which seems to take awhile), I figure it's best to get the pending solution out.

From https://github.com/openzfs/zfs/pull/9961

A patch file from https://github.com/void-linux/void-packages/pull/20506.patch is attached