Aside from the cross-compilation, which is most definitely part of the process but has not yet been explored in depth[^1], nothing in your build immediately sticks out at as problematic, but i've bookmarked it for future reference during the port.
The .bat build (Windows) will not change via this port. Only Unix-like environments will potentially be affected.
> Is there a [multi-stage] Dockerfile to build, install and test SQLite with the new build system?
Not that the sqlite project maintains, no. None of us use docker in any capacity. We work only from the canonical source tree and we like to think that it's easy enough to do that other folks can too.
> Is there SLSA signing for the SQLite build artifacts?
That's out of scope for, and unrelated to, this particular sub-project.
> slsa-framework/slsa-github-generator: https://github.com/slsa-framework/slsa-github-generator
says:
> This repository contains free tools to generate and verify SLSA Build Level 3 provenance for native GitHub projects using GitHub Actions.
We don't use github except to post a read-only mirror of the canonical source tree.
[^1]: Autosetup has strong support for cross-compilation, it just hasn't yet been tested in the being-ported build process.