[llvm] [RISC-V][MC] Reject x0 as the temporary register for store pseudos (PR #227512)

[Alexander Richardson via llvm-commits]

arichardson wrote:

> Oh yes thats a good point. I didn't notice the other ones since this was the one I hit while updating my RVY patch set. Will update this to also fix the other ones.

thanks for the suggestion, added all (I think) the other ones now.

https://github.com/llvm/llvm-project/pull/227512