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

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

Thanks for the updates. It is looking close.

I think we would be best to avoid using mapping symbols as relocation targets as that is not permitted in the AArch64 ABI, and this can be exposed to other tools with `-emit-relocs`. I've made a suggestion to use the Section Symbol which could be used instead of mapping symbols. Should not need a lot more code.

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