Create a macOS universal binary

[baronfel]

Adds a target that

• creates arch-specific macos binaries
• stitches them together using lipo to create a universal binary (thanks @rolfbjarne!)

Things we need to think about:

• how are these signed/notarized?
• how is the universal binary passed to the rest of the build process in the azdo pipelines?
• How does the azdo pipeline on mac call the build? Because we'd need it to either call this new target directly or have this target be a dependency of the existing build entry point

cc @joeloff / @marcpopMSFT

[rolfbjarne]

I don't know if you care, but this won't work if any of these paths have spaces in them.

[baronfel]

Tested this on a m2 machine and it works as expected:

% file dotnet-core-uninstall 
dotnet-core-uninstall: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64:Mach-O 64-bit executable arm64]
dotnet-core-uninstall (for architecture x86_64):	Mach-O 64-bit executable x86_64
dotnet-core-uninstall (for architecture arm64):	Mach-O 64-bit executable arm64

[joeloff]

Don't think we do notarization for this.

[joeloff]

who/what calls this target?

[baronfel]

I need help making the macOS build call this - it's one of the questions in the issue description :)

[joeloff]

probably here: https://github.com/dotnet/cli-lab/blob/25e91f1d39ad446131c0fe4bc998c5a33e766773/.vsts-ci.yml#L137C1-L144C33

You can tweak the .yml, then push your branch internal to trigger an official build against your branch, that's the only way to verify yaml changes