link with libstdc++.so.5 using gcc4

I have ubuntu (gcc (GCC) 4.0.3 (Ubuntu 4.0.3-1ubuntu5)) with libstdc++.so.6

The target platform is RHEL3 with libstdc++.so.5. How can I crosscompile my C++ application using gcc4 but link with libstdc++.so.5 instead of libstdc++.so.6?