Enable Windows-on-ARM64 builds by fixing arch detection and adding Windows ARM CI

[tsomanna]

Issue

Several AWS CRT projects rely on builder.pyz for builds (e.g., aws-c-event-stream). Today, when builder.pyz runs on a Windows ARM64 machine, architecture detection reports x64, which blocks native ARM64 workflows and prevents downstream projects from producing native ARM64 artifacts.

Adding Windows ARM64 support here improves developer experience and reduces dependency on x64 emulation for Windows-on-ARM platforms.

Description of changes:

1. Windows ARM64 host detection (builder/core/host.py)

• Use platform.machine() on Windows to detect ARM64
• Map Windows ARM64 to the builder’s canonical internal arch: armv8

2. Windows ARM64 platform + compiler support (builder/core/data.py)

• Add armv8 to MSVC architectures with CMake args -AARM64
• Add windows-armv8 to the platform set
• Extend Windows alias generation so the following map to windows-armv8:
  • windows-arm64, windows-arm64v8, windows-arm64v8a, windows-aarch64

3. CI coverage (.github/workflows/sanity-test.yml)

• Add a Windows ARM runner (windows-11-arm) to the sanity test matrix to ensure this code path is exercised in CI.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[tsomanna]

Hi, any updates on this?

[xiazhvera]

Hi @tsomanna, unfortunately, we don't currently have the bandwidth to review and tests the changes. Windows ARM64 support is on our roadmap, however, we don't have a timeline to share at this point.

[tsomanna]

Hi @xiazhvera, we'd be happy to help you out with testing. Let us know if that works for you and what tests you'd like us to run.