libs-base/Source/ObjectiveC2
..
blocks_runtime.h
blocks_runtime.m
COPYING
GNUmakefile
properties.m
README
runtime.c
runtime.h
sync.m

ObjectiveC2.framework implements the new Apple runtime APIs, introduced with OS X 10.5 on top of the GCC Objective-C runtime.  Its use is now discouraged.  This code has been merged into the GNUstep Objective-C runtime, which can act as a drop-in replacement for GCC libobjc.  You can find the code here:

svn://svn.gna.org/svn/gnustep/libs/libobjc2/trunk