[PATCH] SEH exceptions on Win64 (LLVM)

[Charles Davis]

@vadimcn:
You are more than welcome to go ahead with this (pending approval to commit). I don't have a lot of time to devote to this right now.

Everyone:
This was originally my code, but from the looks of it, it's been heavily modified. I don't even recognize some parts of it anymore. I'm passing whatever little ownership over this patch I had left over to whomever will take it (probably @vadimcn, since that's whom Kai blessed).

http://reviews.llvm.org/D3418