[llvm] [RISCV] Handle zeroinitializer of vector tuple Type (PR #113995)

[Brandon Wu via llvm-commits]

4vtomat wrote:

I added a `ISD::BITCAST` case in `PreprocessISelDAG`, but somehow the git diff made it looks like I also changed the code in `ISD::SPLAT_VECTOR` case lol

https://github.com/llvm/llvm-project/pull/113995