[PATCH] Initial SEH IR generation implementation

[Reid Kleckner]

>>! In D5607#5, @ABataev wrote:
> Reid, 
>> __try body outlining with noinline and optnone.
> You can use CapturedStmt for body outlining. It works just like Lambdas, but all captured vars are passed by reference 

Thanks, I actually tried that in a subsequent patch layered on this one. It worked great, but Richard isn't particularly happy with the direction. He feels that CapturedStmt is an implementation artifact that shouldn't be in the AST because it doesn't reflect anything user-written. On the other hand, IMO the AST already has explicit nodes for implicit things that the user didn't write, such as MaterializeTemporaryExpr. I will probably try doing outlining during IRGen to compare the approaches.

http://reviews.llvm.org/D5607