This patch provides preliminary support for non-fragile instance variables on the GNU runtime.

It currently requires a patches to GNU libobjc (and so is not enabled by default) which are currently 
being tested and reviewed by GNUstep before being pushed upstream.
This patch does not allow support for synthesized ivars, but does provide the infrastructure 
needed for supporting them.
Patch by David Chisnall

llvm-svn: 72175