[VMR] Linux Vertical Build PoC

[steveisok]

Objective

As part of https://github.com/dotnet/arcade/blob/main/Documentation/UnifiedBuild/UB-Roadmap.md, we want to produce vertical builds for linux-x64 and linux-arm64 in order to flush out any problematic areas and continue to shape our VMR approach for .NET 9.

Outcomes

• The PoC can produce the customer facing artifacts that .NET produces in its current official build (or we know we can produce such an artifact by completing a specified set of work).
• Issues are filed providing a clear path between the PoC and productization of the VMR vertical
• A rolling CI leg is added to the VMR to identify breaks in the PoC

Work Items

• Source-build should support CBL Mariner #3654
• [VMR] Add cross build support #3671 - in order to target arm64 and other architectures different from the build host
• Build linux-x64
• Build linux-arm64
• Build linux-arm
• Add CI legs for linux-x64, linux-arm, and linux-arm64

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[mmitche]

@steveisok Can we close this out at this point?

[tkapin]

Closing as agreed with @steveisok