O Steam vem com suas próprias bibliotecas do gcc, que estão desatualizadas e não funcionam em distribuições com bibliotecas mais novas. Para mais informações, confira: link
Para resolver seu problema no Ubuntu 14.04, feche o Steam e execute:
rm ~/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/lib/x86_64-linux-gnu/libgcc_s.so.1
rm ~/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/usr/lib/x86_64-linux-gnu/libstdc++.so.6
rm ~/.local/share/Steam/ubuntu12_32/steam-runtime/i386/lib/i386-linux-gnu/libgcc_s.so.1
rm ~/.local/share/Steam/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libstdc++.so.6
rm ~/.local/share/Steam/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libxcb.so.1
No dia 14.10, o caminho mudou, os comandos são semelhantes:
rm ~/.steam/ubuntu12_32/steam-runtime/amd64/lib/x86_64-linux-gnu/libgcc_s.so.1
rm ~/.steam/ubuntu12_32/steam-runtime/amd64/usr/lib/x86_64-linux-gnu/libstdc++.so.6
rm ~/.steam/ubuntu12_32/steam-runtime/i386/lib/i386-linux-gnu/libgcc_s.so.1
rm ~/.steam/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libstdc++.so.6
rm ~/.steam/ubuntu12_32/steam-runtime/i386/usr/lib/i386-linux-gnu/libxcb.so.1
ou
rm ~/.steam/bin32/steam-runtime/amd64/lib/x86_64-linux-gnu/libgcc_s.so.1
rm ~/.steam/bin32/steam-runtime/amd64/usr/lib/x86_64-linux-gnu/libstdc++.so.6
rm ~/.steam/bin32/steam-runtime/i386/lib/i386-linux-gnu/libgcc_s.so.1
rm ~/.steam/bin32/steam-runtime/i386/usr/lib/i386-linux-gnu/libstdc++.so.6
rm ~/.steam/bin32/steam-runtime/i386/usr/lib/i386-linux-gnu/libxcb.so.1