[llvm] [NFC][MC][XCore] Rearrange decoder functions for XCore disassembler (PR #155009)

[Rahul Joshi via llvm-commits]

jurahul wrote:

Thanks, I lied  :( The moved set of functions are also shuffled around a bit to avoid forward declarations within themselves (there were uses before definitions and I fixed them by rearranging the functions. No other code changes though. I updated description to mention that.

https://github.com/llvm/llvm-project/pull/155009