[lld] [lld-macho] Include branch extension thunks in linker map (PR #120496)

[Carlo Cabrera via llvm-commits]

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

Not super familiar with this part of LLD, so would be good to get an approval from someone else. But looks reasonable to me as far as I can tell.

https://github.com/llvm/llvm-project/pull/120496