[lld] [lld-macho] Fix crash with DWARF section-relative relocations (PR #168075)

[Joel Reymont via llvm-commits]

joelreymont wrote:

This PR attempts to prevent `lld-macho` from crashing when it encounters DWARF section‑relative relocations. Today, OCaml’s DWARF output can produce relocations that `lld` doesn’t rewrite correctly, and `dsymutil` rejects or strips them, leaving linked Mach‑O binaries (and dSYMs) without usable debug info. 

The change adjusts `lld`’s handling of these relocations so DWARF is preserved end‑to‑end: no crash during linking, relocations rewritten properly for `dsymutil`, and the final binary/dSYM retains complete debug info. 

This avoids having to skip or downgrade post‑link DWARF checks due to missing debug sections.

https://github.com/llvm/llvm-project/pull/168075