Ship pre-built LLVM libraries in the repository to simplify the build process

[feds01]

Currently, we require that the host system of the compiler must include an installation of LLVM. This is inconvenient and leads to problems such as (#825). We could explore trying to ship the compiler with Mac/Linux/Windows pre-built binaries, however, this might turn out to be more work than benefit; we need to investigate the feasibility of this approach.