[llvm] Reapply "[LLVM][TableGen] Parameterize NumToSkip in DecoderEmitter" (#136017) (PR #136019)

[Rahul Joshi via llvm-commits]

jurahul wrote:

The repro I currently have is the expensive check enabled build of LLM, which takes a really long time to build. But it could be a GCC vs clang thing and I can try to reproduce by just building with gcc (though I'd have though we have lots of bots that build with gcc). I did confirm that with all other things constant, changing that namespace in DecoderEmitter from anonymous to llvm makes the failure appear again. 

https://github.com/llvm/llvm-project/pull/136019