With Tests on, I get this error from the libobjc build.
Linking C executable Test/AllocatePair
/usr/local/bin/clang \
-std=gnu99 \
-fexceptions \
Test/CMakeFiles/AllocatePair.dir/AllocatePair.m.o \
-o Test/AllocatePair \
libobjc.so.4.6 \
-lsupc++ -Wl,-rpath,/home/frank/objc/build -1.7-RC1
libobjc.so.4.6: undefined reference to `vtable for std::type_info'
libobjc.so.4.6: undefined reference to `std::type_info::__is_function_p() const'
libobjc.so.4.6: undefined reference to `typeinfo for std::type_info'
libobjc.so.4.6: undefined reference to `std::type_info::~type_info()'
libobjc.so.4.6: undefined reference to `std::type_info::__do_upcast(__cxxabiv1::__class_type_inf
o const*, void**) const'
libobjc.so.4.6: undefined reference to `std::type_info::__is_pointer_p() const'
clang-3.4: error: linker command failed with exit code 1 (use -v to see invocation)