Ensure version alignment of multi-arch GCC base libraries to prevent libc6:arm64 / libgcc-s1 conflicts during cross-compilation setup

[anuchandy]

My…

What does this PR do?

[Provide a clear, concise description of the changes]

This PR fixes version conflicts when installing the arm64 cross-compilation toolchain on an amd64 Ubuntu host. The root cause was that certain core libraries, such as libgcc-s1, gcc-*-base, are marked Multi-Arch: same, which means they must be installed at the exact same version across all enabled architectures (here amd64 (the host) and arm64). Previously, while installing libc6:arm64, the apt could resolve a ibgcc-s1:arm64 to a different or newer version than libgcc-s1:amd64, leading to conflicts.

The original CI failure was

[Any additional context, screenshots, or information that helps reviewers]

See the original error here
[Any additional context, screenshots, or information that helps reviewers]

GitHub issue number?

[Link to the GitHub issue this PR addresses]

Pre-merge Checklist

• Required for All PRs
  • Read contribution guidelines
  • PR title clearly describes the change
  • Commit history is clean with descriptive messages (cleanup guide)
  • Added comprehensive tests for new/modified functionality
  • Updated CHANGELOG.md for product changes (features, bug fixes, UI/UX, updated dependencies)
  • Spelling check passes: .\eng\common\spelling\Invoke-Cspell.ps1
• For MCP tool changes:
  • One tool per PR: This PR adds or modifies only one MCP tool for faster review cycles
  • Updated README.md documentation
  • Updated command list in /docs/azmcp-commands.md
  • Updated test prompts in /docs/e2eTestPrompts.md
  • For new or modified tool descriptions, ran the eng/tools/ToolDescriptionEvaluator tool and obtained a result >= 0.4
• 👉 For Community (non-Azure team member) PRs:
  • Security review: Reviewed code for security vulnerabilities, malicious code, or suspicious activities before running tests (crypto mining, spam, data exfiltration, etc.)
  • Manual tests run: added comment /azp run azure - mcp to run Live Test Pipeline

[Copilot]

Pull Request Overview

This PR fixes multi-architecture package version conflicts when setting up ARM64 cross-compilation toolchain on AMD64 Ubuntu hosts. The issue occurred because certain core libraries marked as "Multi-Arch: same" (like libgcc-s1, libc6, and gcc-*-base) must be installed at identical versions across all enabled architectures, but the previous implementation allowed version mismatches that caused installation failures.

Key changes:

• Implements version alignment logic to find and install matching versions of Multi-Arch packages
• Adds proper repository configuration to separate AMD64 and ARM64 package sources
• Includes verification steps to ensure successful installation

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
eng/scripts/Install-LinuxArm64CrossCompileToolchain.ps1	Complete rewrite of bash script to handle Multi-Arch package version alignment and proper repository configuration
.vscode/cspell.json	Added spelling exceptions for technical terms used in the updated script

[joshfree]

nit: would be nice to comment the regex, it's more complicated than I was expecting