Use Arm64 Windows runners for aarch64-msvc CI jobs

[dpaoliello]

Proposal

GitHub is now offering free Arm64 Windows runners (with tooling preinstalled): https://github.com/orgs/community/discussions/155713

Rust's CI should add new aarch64-msvc jobs (mirroring the existing x86_64-msvc jobs) using these new runners AND switch the existing dist-aarch64-msvc job to also use the new runners.

I've verified that these jobs will work and already merged the necessary fixes.

The final piece of this is to add the aarch64-msvc jobs themselves, and switch dist-aarch64-msvc: rust-lang/rust#140136

Mentors or Reviewers

@Kobzol has been reviewing these changes

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

[rustbot]

Important

This issue is not meant to be used for technical discussion. There is a Zulip stream for that.
Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

Concerns or objections can formally be registered here by adding a comment.

@rfcbot concern reason-for-concern
<description of the concern>

Concerns can be lifted with:

@rfcbot resolve reason-for-concern

See documentation at https://forge.rust-lang.org

cc @rust-lang/compiler

[Noratrieb]

As mentioned on Zulip, an MCP like this is the wrong avenue for this.
Switching runners is purely an infra concern and just needs an r+, adding more CI tests means promoting the target to tier 1 and needs an RFC referencing the target tier policy.

Therefore, I'm gonna close this.