[lld] [ELF] -r --compress-debug-sections: update addends for .debug_* sections relocated by REL (PR #66804)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

Thanks for the patch! It resolves the build issue I was observing that lead to the report in  #66738.

One thing I've noticed is that now the build succeeds, but we have a stream of warnings from lld that look like:
```
ld.lld: warning: vmlinux.a(drivers/i2c/busses/i2c-i801.o):(.discard.retpoline_safe+0x120): has non-ABS relocation R_386_PC32 against symbol ''
```
(maybe 200 of these warnings are printed).

Let me do some testing to see if it's related to a specific kernel configuration or what.  It's not clear to me yet if there's more than one bug here, or if this PR is improving one thing while regressing another.

I'll also do further testing on 32b arm targets that we were also observing errors with.

https://github.com/llvm/llvm-project/pull/66804