[llvm] [JITLink][RISCV] Use hashmap to find PCREL_HI20 edge (PR #78849)

[Jonas Hahnfeld via llvm-commits]

hahnjo wrote:

> In the future I think we'll want to have edges sorted by offset (perhaps for performance we'll only sort lazily when needed), so it might be worth adding a comment to revisit this if / when we do start sorting edges.

Yes, I considered that. It's maybe a bit trickier because passes can add edges on the fly (?), but on the other hand, even sorted offsets doesn't get us to constant lookup times as we have with the maps...

https://github.com/llvm/llvm-project/pull/78849