I think the main problems would be around the configure, Make, and autogen files. as said-probably a change in -Werror.
Thanks for report it, from a fast look I saw that latest upstream cjs rebase from gjs didn't update the build-deps, after there is a commit that fixes build issue I hadn't spotted in new packages review:
https://github.com/linuxmint/cjs/commit/ea081f3272d5dfb78eceef47826acf90db5d4bdd
Try add these, should will solve the build issue:
* Add missing libxml2-utils builddepends * Add disable-Werror option to rules