[llvm] [AVR] Fix parsing & emitting relative jumps (PR #102936)

[via llvm-commits]

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

LGTM, with a few nits.

I hope this fix can be merged and backported into LLVM 19 before the release!

https://github.com/llvm/llvm-project/pull/102936