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

[Nico Weber via llvm-commits]

nico wrote:

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

(This is with the sed fix attempt.)

Please take a look and revert for now if it takes a while to fix.

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