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

[Lang Hames via llvm-commits]

https://github.com/lhames approved this pull request.

Looks good to me.

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.

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