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

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

Commit 1 should be a real commit to the tree, i.e. not squashed as part of merging this PR. Commits 2 and 3 should be one commit, i.e. squash and merge is right here. Though it's a bit odd you chose to split them out into separate commits in the PR in the first place.

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