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

https://github.com/Piraty/void-packages cross-aarch64-musl-stddef-fix
https://github.com/void-linux/void-packages/pull/24307

cross-aarch64-linux-musl: do not remove gcc's stddef.h
224951e9dd7820f31ffce0fbe853e860bb37accc forgot to touch aarch64-musl,
possibly because it was added around that time.

A patch file from https://github.com/void-linux/void-packages/pull/24307.patch is attached