[llvm] [RFC][TableGen] Restructure TableGen Source (PR #80847)

[Nico Weber via llvm-commits]

https://github.com/nico commented:

Nice!

An old wish I had back when chapuni introduced llvm-min-tblgen: It'd be nice if llvm-min-tblgen had its own directory, so that we don't need the `PARTIAL_SOURCES_INTENDED` kludge. Looks like this is even easier to do after this change :)

https://github.com/llvm/llvm-project/pull/80847