Implement Vertical Build for MacOS x64 Mono LLVMJIT

[mmitche]

This issue covers productization of the following vertical: MacOS x64 Mono LLVMJIT

• Build OS: MacOS
• Target OS: MacOS
• Build OS Arch: x64
• Target Arch: x64
• Stack Type: Short
• Key Artifacts: MacOS x64 Mono LLVM Runtime Packs

Implementation of this vertical may depend on completion of other items within the Unified Build Space:

• Link issues as necessary

When complete, the following will be true:

• The vertical builds successfully and required changes are backported to individual repos.
• The vertical's outputs are verified as being complete and correct as compared to the current .NET official build.
• The vertical is enabled in VMR rolling CI and PR (if applicable).

T-Shirt Size: Small (default, update as necessary)

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.