Currently when the objc testsuite is run on Darwin PPC, the wrong (system) libobjc is linked in rather than the correct libobjc-gnu shared library. This problem is described on the gcc mailing list at... http://gcc.gnu.org/ml/gcc/2006-09/msg00286.html and makes any test results for objc on Darwin invalid.
You are wrong. There are two Objective-C runtimes. One is the GNU runtime and one is the NeXt^wApple runtime. Darwin defaults to the NeXt runtime. Just PPC64 Darwin does not include a 64bit version of the NeXT Runtime. The two runtimes have differnet slightly different functions.