[llvm] [RISCV] Implement Relaxation for Xqcilb Jumps (PR #142702)

[Sam Elliott via llvm-commits]

lenary wrote:

(Just to clarify, we don't intend to do any codegen changes in this PR - if we do them, it will be at/around the time we start generating Xqcilb which we don't currently do)

https://github.com/llvm/llvm-project/pull/142702