[lld] [ELF] Rename target-specific RelExpr enumerators (PR #118424)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> Perhaps RE_* to match RelExpr? REL_ feels a lot like actual ELF things still.

Thanks for the suggestion. `RE_*` looks better. Updated.



https://github.com/llvm/llvm-project/pull/118424