[llvm] [RISCV] Attach an implicit source operand on vector copies (PR #126155)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

> MIR test would be helpful, it's a huge pain to get this right and you need to consider kill and undef flags

Done

https://github.com/llvm/llvm-project/pull/126155