libretro.uzem: init at 0-unstable-2026-04-20

[KaiStarkk]

Addition of the Uzem core for libretro to support emulating Uzebox in RetroArch.

Packaging notes

• The source is the canonical libretro/libretro-uzem repository, pinned to its latest revision dated 2026-04-20.
• The core declares itself MIT-licensed in uzem_libretro.info, and the Uzem sources compiled by Makefile.common carry MIT license headers. The repository also contains GPL-2.0-or-later GDB server sources, but those files are not part of the libretro source list and the core is compiled with NOGDB.
• GIT_VERSION is supplied from the pinned revision so the upstream Makefile does not attempt to invoke Git in the isolated build environment.
• mkLibretroCore supplies the supported platforms and Libretro team ownership metadata and installs the resulting uzem_libretro shared library in RetroArch's core directory.
• On x86_64-linux, the packaged core was loaded in RetroArch with the official Uzebox repository's tools/packrom/Test/arkanoid.uze, ran for 180 frames, saved SRAM, unloaded cleanly, and exited successfully.
• nixpkgs-review was not completed and is intentionally left unchecked below.

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.
• Follows the automation/AI policy.

The package and this pull request description were prepared with assistance from OpenAI Codex (GPT-5) and reviewed through a successful x86_64-linux package build, formatting checks, and a RetroArch smoke test running the official Uzebox repository's arkanoid.uze for 180 frames.