[llvm] [SystemZ][z/OS] yaml2obj for header and end records (PR #73859)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

As before, I've avoided looking at the GOFF details and just tried to focus on style and test comments, aside from some more (small) general issues too.

https://github.com/llvm/llvm-project/pull/73859