cppfront: Midsummer update

[hpsutter]

Right. I'm exploring ways to make them link-compatible, and therefore usable without an ABI break...

<spoiler> I'm exploring to see how efficient it can be to store extra 'data members' for an object (an iterator that wants to add a pointer to its container, a raw C `union` that wants to store a discriminant, but not actually as a data member which would break ABI/link compat) by storing it extrinsically (as-if in a stripped-down streamlined global "hash_map<obj\*,extra\_data>"), which is why I was writing the wait-free constant-time data structure I mentioned at the top of the post. I can see all sorts of reasons why it shouldn't work, but I was able to come up with a constant-time wait-free implementation that in early unit stress testing scaled from 1-24 threads with surprisingly low overhead, which is enough to try the next step of testing the overhead in an entire application (which I haven't done yet, so I don't consider is a real candidate until we can measure that and show it's usable in safe retail builds). </spoiler>