I made some changes on http://llvm.org/apt/ for the last 2 months.

• Added trusty, Ubuntu 14.04, as a new supported distribution (on the request of Michael Larabel, Phoronix)

• Support both the stable and development version. Currently, that means that the release_34 branch and the trunk are built. So, for example, clang-3.4 and clang-3.5 can be installed.
  release_34 are only built when a new commit is submitted in this branch. trunk is built twice a day.

• Add a new package llvm-{3.4,3.5}-tools which contains various tools to build software/packages on top of llvm. Contributed by Martin Nowack in the context of Klee.

• Since a C++ 11 compiler is now mandatory, I had to force the usage of a backported gcc/g++ 4.8 (thanks Doko).
  This is the case for Ubuntu Precise (12.04), Quantal (12.10) and raring (13.04).
  The thing is that it triggers a dependency on the libstdc++ 4.8 causing the PPA to be mandatory.
  deb http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu $DISTRIBUTION main
  
  For now, because of the lack of backport of gcc 4.8, I am not providing support for Debian stable (wheezy).