Add -static-libgcc -static-libstdc++ to CMakeLists.txt

@oxtopus @rhyolight This worked on CentOS 6.5 with GNU 4.8. I build nupic.core in $NUPIC_CORE (/home/ec2-user/tmp/nupic.core)

After that, I could build NuPIC by running this : ```python setup.py develop --install-dir="$REPOSITORY/build/release/lib/python2.7/site-packages" --cmake_options="-DNUPIC_CORE=${NUPIC_CORE}/build/release"```
${STDLIB} is duplicated on this line.