There's a merged pull request on the void-packages repository

chroot-grep: patch out problematic warnings in egrep and fgrep.
https://github.com/void-linux/void-packages/pull/41593

Description:
This mirrors the changes from grep in https://github.com/void-linux/void-packages/commit/ef5ffe4d696b31041c272be92e912fb454c075ac into chroot-grep.