you have held broken packages. Então, talvez você devesse sudo apt-get clean && sudo apt-get update primeiro.
Eu digito sudo apt-get install libc6-dev e obtenho o seguinte:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if yo uare using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
lib6-dev : Depends: libc6 (= 2.19-0ubuntu6) ut 2.19-0ubuntu6.1 is to be installed
Recommends gcc but it is not going to be installed or c-compiler
E: Unable to correct problems, you have held broken packages.
Estou executando o 14.04.1, que é o mais recente disponível no link
you have held broken packages. Então, talvez você devesse sudo apt-get clean && sudo apt-get update primeiro.