[lld] Migrate away from PointerUnion::dyn_cast (NFC)#123891

kazutakahirata merged 1 commit intollvm:mainllvm/llvm-project:mainfrom

kazutakahirata:cleanup_001_PointerUnion_lld_MachOkazutakahirata/llvm-project:cleanup_001_PointerUnion_lld_MachOCopy head branch name to clipboard