r319297 - Toolchain: Normalize dwarf, sjlj and seh eh

[Martin Storsjö via cfe-commits]

On Wed, 29 Nov 2017, Martell Malone via cfe-commits wrote:

> Thanks for letting me know Reid.
> I’ll in work and won’t be able to access the repo until lunch time. (~3
> hours)
> Feel free to revert if it is not trivial.
> 
> The easy fix might be to change to == x86_64 from != x86 For is Windows in
> the default toolchain. That should restore the old behavior.

My suggestion would be to just return None for all architectures for the 
default windows (msvc) case. We didn't use to set any defines to indicate 
EH mode there before anyway, so setting it to None should make things 
behave just as before, right?

// Martin