[llvm] [TableGen] Add a backend to generate MacroFusion predicators (PR #72222)

[Pierre van Houtryve via llvm-commits]

https://github.com/Pierre-vh commented:

Not part of the review but adding some nits/comments.

I also think it would be nice if this backend had at least one test to track the expected codegen, and see codegen changes. It makes future maintenance a lot easier if we can see what changes do to codegen during a review.

https://github.com/llvm/llvm-project/pull/72222