[lld] Fix lld crash wrt generated thunks growing away from the patched code (PR #170495)

[Peter Smith via llvm-commits]

https://github.com/smithp35 approved this pull request.

This looks good to me. Thanks for all the updates.

I'll leave some time to see if @MaskRay has any further comments. 

https://github.com/llvm/llvm-project/pull/170495