[WIP] libobjc2 new ABI

[David Chisnall]

Hello,

The Christmas before last, I started working on a complete cleanup and redesign 
of the GNUstep Objective-C ABI.  This is motivated by the need to make some 
incompatible changes to support some newer features and by a desire to make use 
of post-1988 linker features to reduce object code size.

Progress on this has been slow.  I basically didn’t work on it at all for a 
year, then made more progress last Christmas, had another six months of being 
too busy, did a small amount over the summer, and then got back to it this 
Christmas.  I’ve also started properly documenting the ABI (though this is also 
very incomplete!).

The code is in two repos for the runtime and clang parts:

https://github.com/davidchisnall/libobjc2 (newabi branch)
https://github.com/davidchisnall/clang-gnustep-abi-2

Some things are probably broken (though the runtime is now able to pass all of 
its own tests with both -fobjc-runtime=gnustep-2.0 and 
-fobjc-runtime=gnustep-1.7), but if anyone wants to follow the development (or 
contribute patches!) they’re very welcome!

David