[llvm] Support replacing `add rd, Zero, Zero` with `c.li rd, 0` (PR #86937)

[Wang Pengcheng via llvm-commits]

https://github.com/wangpc-pp commented:

I'm not opposed to add this, but in what case will we generate `add rd, zero, zero`?
I think we will generate `addi, rd, zero, 0`.

https://github.com/llvm/llvm-project/pull/86937