[PATCH]: Add a flag to the DWARF Compile Unit to indicate if it was compiled with ARC

[Adrian Prantl]

>> I am happy to leave you and Adrian to decide the best representation as long as you agree that this is important to represent *somehow*. I was under the impression that that was in question.
>> 
> 
> Nah, language features are important to represent in dwarf. :)

I’m happy to search for the best representation in DWARF.
Going through John’s earlier examples, “weak” vs. “strong” can definitely be represented as an attribute.

But I think that the last three (especially the “monitor retain/release events”) cases actually do warrant at least a per-function "ARC-enabled" attribute. But since we can only turn on ARC on a per-compilation-unit basis we might as well stick with the cu-wide flag and save some space.
Let me know if you see an opportunity to break this down into smaller attributes that I missed.

-- adrian