[llvm] [dwarf] make dwarf fission compatible with RISCV relaxations 1/2 (PR #166597)

[via llvm-commits]

daniilavdeev wrote:

I've rolled back to `isRangeRelaxable` variant, take a look, please.

> It would be good if you could summarise your analysis above into comments on the functions themselves

Yep, I've added an appropriate comment on the `isRangeRelaxable` function and a corresponding comment in debug emission logic explaining why we can't use `absoluteSymbolDiff` instead.

One thing I'm not sure about is where to place `isRangeRelaxable` function. Maybe you know a better place for it than `MCSymbol.h`? On the other hand, I don’t think it’s particularly significant, so we can leave it as it.

https://github.com/llvm/llvm-project/pull/166597