[llvm] [RISCV] Implement trampolines for rv64 (PR #96309)

[Roger Ferrer Ibáñez via llvm-commits]

rofirrim wrote:

The test has changed because we used to coalesce the two `sw` into a single `sd`. I assume this is still reasonable, though.

https://github.com/llvm/llvm-project/pull/96309