x86_64-linux builder for darwin is slow; no Rosetta

[roberth]

          > I'm concerned that this might lock mac users into a solution with [worse](https://stackoverflow.com/questions/73605175/why-cant-qemu-get-even-close-to-rosetta-2s-performance-when-translating-x86-to) performance, only some people knowing that it's slower than necessary and even fewer people knowing how to fix it.

What I recall from @sandydoo is that Rosetta 2 can run in Apple Virtualization Framework but not QEMU. See virtualisation.rosetta.enable.

What if we could launch UTM instead of qemu? It seems to have gained a CLI recently.

As the linux-builder is ephemeral, my preference would be to merge this despite being slow and leaving it as future work to speed it up which could be done without changing the interface.

Another way we could speed this up in the future is building QEMU with Virtualization support and using Rosetta (currently the patchset isn’t mainlined and don’t yet have the correct entitlements necessary to run Rosetta).

Originally posted by @Enzime in #262021 (comment)

[arianvp]

I've been working on a lightweight CLI for running NixOS VMs using Rosetta and use this actively as my builder:

• https://github.com/arianvp/server-optimised-nixos/tree/runvf-rewrite/runvf

The blocker for upstreaming is that nixpkgs doesn't have a modern enough MacOS SDK for it to compile.

[roberth]

MacOS SDKs have been a subject of the macOS collective.
Also there's

• apple_sdks: init with 11.1, 11.3, 12.1, 12.3, 13.1, and 13.3 #229210
• perhaps more tangentially Discussion: The future of SDKs on Darwin #242666 (comment)