the parameter to apt-get is always a package name, never a URL
to install a package from launchpad, you can do a couple of things
create a new source repo and then install the package
download the specific .deb package and install that.
the URL you list is something I don't have permission to access, which makes it a little hard to help you
It's possible that the cross compiler isn't available to run on the pi
but on my pi, I can find the package
do an apt-get update before you try to install any packages