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

[Patryk Wychowaniec via llvm-commits]

Patryk27 wrote:

I'm cleaning up the pull requests - this change has already been merged, we're missing just the second commit, which I'll extract into a separate pull request now.

I'm also noting both your suggestions and I'll try to prepare a fix where `+2` doesn't leak into objdump's output and where we generate relocations, to be in accordance with gcc.

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