[lld] [lld][MachO] Preserve class-address addends in ObjC category merging (PR #211431)

[Karim Alweheshy via llvm-commits]

karim-alweheshy wrote:

@alx32 @int3 Could you please review this Mach-O Objective-C category-merging fix? It preserves residual class-address addends when the exact Swift class alias disappears, while retaining the defensive handling for genuinely missing metadata. Focused regressions and exact-head CI are green. Thanks!

https://github.com/llvm/llvm-project/pull/211431