[lld] [lld-macho] Add support for category names in ConcatInputSection's (PR #90850)

[Kyungwoo Lee via llvm-commits]

================
@@ -186,13 +186,23 @@ ObjcCategoryChecker::ObjcCategoryChecker()
       roClassLayout(target->wordSize), listHeaderLayout(target->wordSize),
       methodLayout(target->wordSize) {}
 
-// \p r must point to an offset within a cstring section.
+// \p r must point to an offset within a CStringInputSection or a
+// ConcatInputSection
 static StringRef getReferentString(const Reloc &r) {
   if (auto *isec = r.referent.dyn_cast<InputSection *>())
     return cast<CStringInputSection>(isec)->getStringRefAtOffset(r.addend);
   auto *sym = cast<Defined>(r.referent.get<Symbol *>());
-  return cast<CStringInputSection>(sym->isec())
-      ->getStringRefAtOffset(sym->value + r.addend);
+  if (auto *s = dyn_cast_or_null<CStringInputSection>(sym->isec()))
----------------
kyulee-com wrote:

nit: it seems `sym->isec()` is being used in the following code. Can we replace them by a variable? Perhaps the similar thing for  `sym->value + r.addend` which seems representing an offset.
```suggestion
  auto *isec = sym->isec();
  auto offset = sym->value + r.addend;
  if (auto *s = dyn_cast_or_null<CStringInputSection>(isec))
    return s->getStringRefAtOffset(offset);

  if (isa<ConcatInputSection>(isec)) {
    auto strData = isec->data.slice(offset);
    uint32_t len = strnlen((const char *)strData.data(), strData.size());
    return StringRef((const char *)strData.data(), len);
  }
```

https://github.com/llvm/llvm-project/pull/90850