[llvm] [DwarfGenerator] Calculate relative offset according to Dwarf Version (PR #84847)

[Will Hawkins via llvm-commits]

hawkinsw wrote:

> Do you have commit access? You can squash and merge this as soon as you're ready, if so. Alternatively, I can do so if you need me to.

I do, but I am still relatively "new" to the process and hesitant/nervous. If you would be willing to commit, I would appreciate it. 

On the other hand, I have to learn sometime. 

https://github.com/llvm/llvm-project/pull/84847