slang-llvm support for ARM

[jsmall-zzz]

Currently the slang project builds LLVM binaries, that are used to build slang-llvm, which is the preferred mechanism for JIT CPU code.

We build LLVM for the follow targets

• Linux x64
• MacOS x64
• Win x86
• Win x64

Supporting ARM would broaden the usefulness of the capability. The actual ask is for linux primarily. In order of decreasing importance...

• Linux
• MacOS (ideally we'd build a "universal" binary, but that isn't essential)
• Windows

[csyonghe]

Now that we have github actions set up for arm64 on our self-hosted server, using it to build llvm should be possible.

[natduca]

Tentatively putting as nice to have for Q2, but may adjust based on which customers need it

[bmillsNV]

Move to backlog. No customer requests for this feature.