You should be able to add the WPILib toolchain ppa to your apt lists and install with apt-get. The version of the ppa you want to add is dependent on which version of Debian you are running. Something like this:
https://wiki.debian.org/CreatePackageFromPPA. Note that building from source will take a while, so you might try using the binary version first. I recall trusty working on Jessie the last time I tried.