Fix Windows CI: Use pre-installed 7zip on GHA runners

[sosukesuzuki]

Problem

Windows CI is still failing because LLVM installation requires 7zip to extract the installer, and downloads from 7-zip.org fail with SSL errors on GitHub Actions runners.

Solution

GitHub Actions Windows runners have 7zip pre-installed at C:\Program Files\7-Zip. Configure scoop to use this external 7zip:

"C:\Program Files\7-Zip" >> $Env:GITHUB_PATH
scoop config use_external_7zip true
scoop install ninja llvm@19.1.7

This also simplifies the LLVM installation by using the standard llvm@19.1.7 syntax instead of a pinned manifest URL.

[coderabbitai]

Caution

Review failed

The pull request is closed.

Walkthrough

The Windows installation flow for LLVM and Ninja in the build workflow was replaced with a Scoop-based approach. It now uses the pre-installed 7-zip on Windows runners, installs LLVM 19.1.7 and Ninja via Scoop, and updates the PATH configuration accordingly.

Changes

Cohort / File(s)	Change Summary
GitHub Actions Workflow .github/workflows/build-reusable.yml	Updated Windows installation flow for LLVM and Ninja to use Scoop with pre-installed 7-zip, avoiding SSL-pinned downloads. Configures Scoop to use external 7-zip, installs LLVM 19.1.7 and Ninja via Scoop, and updates PATH to include 7-zip and LLVM binaries.

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• .github/workflows/build-reusable.yml

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