[lld] [lld-macho] Improve robustness of ObjC category merging (PR #112618)

[via llvm-commits]

alx32 wrote:

> Looks like this breaks tests on Mac: http://45.33.8.238/macm1/94123/step_9.txt

Repro'ed on Mac + confirmed Fixed on Linux + Mac: https://github.com/llvm/llvm-project/pull/112981
I want to wait for validation to complete before merging because I switched the tool from sed to awk - or should I just merge right away ? 

https://github.com/llvm/llvm-project/pull/112618