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

https://github.com/ericonr/void-packages cflags
https://github.com/void-linux/void-packages/pull/24405

srcpkgs: don't append CFLAGS outside of funtions.
Package templates are sourced multiple times during the build process,
which can lead to issues when defining variables like CFLAGS using
`CFLAGS+=`, since the contents will be added multiple times. This can
lead to a build command with `-static -static`, for example. Adding to
CFLAGS inside functions is safe, since functions are run only once.

A patch file from https://github.com/void-linux/void-packages/pull/24405.patch is attached