Automerge: [Clang][NFC] Code cleanup in CGBuiltin.cpp (#132060)

- Use `Intrinsic::` directly instead of `llvm::Intrinsic::`.
- Eliminate redundant `nullptr` for some `CreateIntrinsic` calls.
- Eliminate redundant `ArrayRef` casts.
- Use C++17 structured binding instead of `std::tie`.

Author: jurahul