Compiling libc++ from within llvm (3.1)

Hi All,
   I am able to compile llvm/clang as well as libc++ individually. I saw that I could put libc++ in llvm/projects directory to compile it as part of llvm. However I see an error when compiling:

[ 51%] Building CXX object projects/libcxx/lib/CMakeFiles/cxx.dir/__/src/algorithm.cpp.o
In file included from /local/mnt/workspace/llvm/src/projects/libcxx/include/algorithm:591:0,
                 from /local/mnt/workspace/llvm/src/projects/libcxx/src/algorithm.cpp:10:
/local/mnt/workspace/llvm/src/projects/libcxx/include/type_traits:731:2: error: #error is_base_of not implemented.

   My command looks:

cmake_args="Unix Makefiles"
cmake -G "$cmake_args" -DLLVM_TARGETS_TO_BUILD="X86" -DCMAKE_BUILD_TYPE="Release" -DCMAKE_INSTALL_PREFIX="../bin" ../src

  Alternatively, I tried to compile llvm/clang with libc++ but couldnt figure out how to pass the '--enable-libcpp' option via cmake.

   Any tips?