Add aarch64-pc-windows-gnullvm target for Rust

[jeroen]

Open source ecosystems based on msys2 use clang-arm64 toolchains , which require the aarch64-pc-windows-gnullvm target in rust. We also need this for the R project.

This is basically the native target on arm64 for most oss projects, it is a bit surprising it is not installed.

[Copilot]

Pull request overview

This PR updates the Windows Rust installation script to ensure the aarch64-pc-windows-gnullvm Rust target is available on ARM64 runner images, improving compatibility with ecosystems (e.g., msys2) that use clang-based ARM64 toolchains on Windows.

Changes:

• Add rustup target add aarch64-pc-windows-gnullvm when building ARM64 Windows images.

[v-davit-ioramashvili]

Thanks for getting to this first, @jeroen 👍 — this is exactly the right fix. I'd opened #14493 for the same target before I spotted yours, so I'm closing mine in favour of this one.

One thing worth adding while we're here: a small assertion in Rust.Tests.ps1 so we notice if the target ever silently drops out of a future image (nothing currently checks installed targets). It touches a file that isn't in your diff, so it can't go in as a one-click suggestion — but here's the snippet if you'd like to drop it in. Equally happy to send it as a small follow-up PR after this merges if you'd rather keep this one minimal.

In images/windows/scripts/tests/Rust.Tests.ps1, after the $rustEnvNotExists block:

$rustTargetNames = if (Test-IsArm64) {
    @("aarch64-pc-windows-msvc", "aarch64-pc-windows-gnullvm")
} else {
    @("i686-pc-windows-msvc", "x86_64-pc-windows-gnu")
}
$rustTargets = $rustTargetNames | ForEach-Object { @{ Target = $_ } }

and alongside the other It blocks:

It "<Target> rustup target is installed" -TestCases $rustTargets {
    (rustup target list --installed) | Should -Contain $Target
}

Either way — thanks again! 🙏