[llvm] [MC][Dwarf] Support DWARF Version 6 in CIE (PR #226997)

[Will Hawkins via llvm-commits]

hawkinsw wrote:

> LGTM
> 
> The alternative was to change the test to use a triple that didn't hit this code, but it's always a shame to make a test less generic so I prefer this.
> 
> Include in the PR description the date of the snapshot you got this from. It'll probably be long gone before we care to look again, but might as well.

I can add a link to the PDF, too. Would that be helpful?

https://github.com/llvm/llvm-project/pull/226997