[lld] r218703 - [mach-o] create __unwind_info section on x86_64

[Tim Northover]

> Ah sorry, I misunderstood which bit of code you were pointing at. I'm
> not entirely convinced Windows is correct there, but there's not much
> we can do even if it is wrong. Should be updated in r220115.

Oh, found the missing link, and Windows is quite right.
[iterator.requirements.general] says dereferencable is equivalent to
*i being valid, and the containers section says v[i] <=> *(v.data() +
i).

Tim.