[llvm] [LLVM][MC][DecoderEmitter] Add support to specialize decoder per bitwidth (PR #154865)

[Rahul Joshi via llvm-commits]

jurahul wrote:

Note, fix for build failure being attempted here: https://github.com/llvm/llvm-project/pull/156375

https://github.com/llvm/llvm-project/pull/154865