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

https://github.com/repk/void-packages php-cross
https://github.com/void-linux/void-packages/pull/20952

php: Add cross compilation support
Support cross compilation by providing builddir path in configure and patching phar and pear makefiles to use host's php binary to install themselves. Therefore it also makes php a hostmakedepends when crosscompiling.

A patch file from https://github.com/void-linux/void-packages/pull/20952.patch is attached