Estou usando o Ubuntu 15.04, aqui o que eu tenho:
...
libstdc++6-4.9-dbg-arm64-cross : Conflicts: libstdc++6-4.8-dbg-arm64-cross but 4.8.4-1ubuntu15cross0.15 is to be installed
libstdc++6-4.9-dbg-armel-cross : Conflicts: libstdc++6-4.7-dbg-armel-cross but 4.7.4-2ubuntu1cross1.86 is to be installed
libstdc++6-4.9-dbg-armhf-cross : Conflicts: libstdc++6-4.7-dbg-armhf-cross but 4.7.4-2ubuntu1cross1.86 is to be installed
Conflicts: libstdc++6-4.8-dbg-armhf-cross but 4.8.4-1ubuntu10cross0.15 is to be installed
libstdc++6-4.9-dbg-powerpc-cross : Conflicts: libstdc++6-4.8-dbg-powerpc-cross but 4.8.4-1ubuntu10cross0.18 is to be installed
libstdc++6-4.9-dbg-ppc64el-cross : Conflicts: libstdc++6-4.8-dbg-ppc64el-cross but 4.8.4-1ubuntu10cross0.7 is to be installed
E: Unable to correct problems, you have held broken packages.
não existe um pacote com o nome libstdc++ consulte aqui . Eu acho que você está procurando libstdc++6 .so instalar usando
sudo apt-get install libstdc++6
ou se você estiver procurando por outra biblioteca que esteja faltando em seu sistema, então procure qual pacote tem essa biblioteca e instale ou extraia esse pacote e copie a biblioteca diretamente.