My test refactoring in D80217 seems to have caused yaml2obj to emit unaligned
nlist_64 structs, causing ASAN'd lld to be unhappy. I don't think this is an
issue with yaml2obj though -- llvm-mc also seems to emit unaligned nlist_64s.
This diff makes lld able to safely do aligned reads under ASAN builds while
hopefully creating no overhead for regular builds on architectures that support
Depends on D80217.