Make a New Logging Service Decoupled From `llvm::dbgs()` and `LLVM_DEBUG`

Currently Luthier uses the `LLVM_DEBUG` mechanism from LLVM defined under <llvm/Support/Debug.h>; However, it will only be enabled if `NDEBUG` was enabled when building LLVM, and it is not reasonable to expect the LLVM used has this enabled. 

Therefore, it would be great to have a logging mechanism that still depends on LLVM streams but is decoupled from LLVM's debug flags. 