[CodeGen] Migrate away from PointerUnion::dyn_cast (NFC)#125456

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

kazutakahirata:cleanup_001_PointerUnion_clang_CodeGen_ItaniumCXXABIkazutakahirata/llvm-project:cleanup_001_PointerUnion_clang_CodeGen_ItaniumCXXABICopy head branch name to clipboard