[PATCH] [lld] [mach-o] implement minimal __unwind_info support

[Tim Northover]

> Now I'm just curious... Why 3? (How did you end up with that
> limitation/number)

2 bits in the (32-bit) compact encoding are devoted to the personality
function, with 0 always implying "no personality". If that overflows,
I think we have to defer to DWARF (which isn't implemented yet).

It's fairly neat, actually. I think I could rant about MachO for
hours, but the final compact unwind encoding probably wouldn't feature
much (intermediate stages get sketchier).

Cheers.

Tim.