vimPlugins.fff-nvim: fix illegal instructions by targetting a baseline CPU

[saadndm]

fff-nvim 0.10 uses zlob 1.6.0, which targets the builder's native CPU by default, making the build impure and causing SIGILL on other CPUs.

This follows dmtrKovalenko/fff#707 and sets CI=1 to target a portable CPU baseline.

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.

[saadndm]

nixpkgs-review result

Generated using nixpkgs-review-gha

Command: nixpkgs-review pr 545572
Commit: 8ce69b14f4621fd64f088704ae2a76e219cd7fc0 (subsequent changes)
Merge: e9af6309669b64d4e2883e11b394fa6996f9c6e8

Logs: https://github.com/saadndm/nixpkgs-review-gha/actions/runs/30156215878

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x86_64-linux

✅ 1 package built:

• vimPlugins.fff-nvim

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aarch64-linux

✅ 1 package built:

• vimPlugins.fff-nvim

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x86_64-darwin

✅ No rebuilds

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aarch64-darwin (sandbox = relaxed)

✅ 1 package built:

• vimPlugins.fff-nvim