Add CI to build LLVM docker image

[lisaong]

What feature are you suggesting?

Overview:

Currently we use a non-official externally-built docker image that contains Accera LLVM libraries to satisfy our build dependencies. The workflow for building that image lives in https://github.com/lisaong/accera-llvm-canary. It should be moved to this repo.

Smaller Details:

Lower priority, but also, consider moving to GitHub container registry rather than Dockerhub

Nature of Request:

• Change

Why would this feature be useful?

Avoid external repo dependencies unless it's a submodule.