[llvm] [llvm] Include LLVM_REPOSITORY and LLVM_REVISION in tool version (PR #84990)

[Reid Kleckner via llvm-commits]

rnk wrote:

I suppose this is a good time to remind folks that the LLVM_APPEND_VC_REV CMake option exists for faster developer builds. It's also worth pointing out that the unsupported gn and Bazel builds do not add the git revision by default, for a faster developer build experience.

I think it's not good enough to move this to another library that Support links against because llvm-tblgen will still depend on it. Going back deep into the past, Zachary Turner recommended that we make a more minimal support library, which is a curated subset of Support that exists juts for tablegen and any other C++ tools that run as part of the build. Support would just depend on this "SupportLite" library, so it would be transparent to most Support users.

https://github.com/llvm/llvm-project/pull/84990