epic: llama.cpp should support `LLVM` for ARM-based CPUs

[dan-menlo]

Goal

• llama.cpp should support LLVM for ARM-based CPUs

Tasklist

• What should be the hardware heuristic to opt for LLVM?
• Should Installer support this?
• This may require us to have cortex engines be able to define a "default" llama.cpp version (if two or more exist)

[dan-menlo]

@eckartal Can you link the Reddit post here (and any other requests for this?)

[eckartal]

@eckartal Can you link the Reddit post here (and any other requests for this?)

Source: https://www.reddit.com/r/LocalLLaMA/comments/1fjpm7j/jan_now_runs_faster_on_cpus/

[dan-menlo]

Closing to handle as part of #1453