[llvm] [RISCV] fix SP recovery in varargs functions (PR #114316)

[via llvm-commits]

dlav-sc wrote:

> Commit 1 should be a real commit to the tree, i.e. not squashed as part of merging this PR.

I've made a separate PR: https://github.com/llvm/llvm-project/pull/114970 

https://github.com/llvm/llvm-project/pull/114316