added an explict library definition for libstdc++ to avoid the following error on Ubuntu 13.04.

/usr/bin/ld: zabbix-api-response-collector.o: undefined reference to symbol '_ZNSs4_Rep10_M_destroyERKSaIcE@@GLIBCXX_3.4'
/usr/bin/ld: note: '_ZNSs4_Rep10_M_destroyERKSaIcE@@GLIBCXX_3.4' is defined in DSO /usr/lib/x86_64-linux-gnu/libstdc++.so.6 so try adding it to the linker command line
/usr/lib/x86_64-linux-gnu/libstdc++.so.6: could not read symbols: Invalid operation