[lld] [lld][ELF] Fix crash when relaxation pass encounters synthetic sections (PR #184758)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay commented:

Thx for catching this. I've thought about an alternative: if we allocate relaxAux for synthetic sections but skip relocDeltas/relocTypes allocation (since sec->relocs() would return an empty array for synthetic sections

However, in relax(): relocs is empty. std::fill_n(nullptr, 0, ...) — technically UB per the standard.

https://github.com/llvm/llvm-project/pull/184758