echo deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-4.0 main\
     >> /etc/apt/sources.list.d/llvm.list
echo deb-src http://apt.llvm.org/trusty/ llvm-toolchain-trusty-4.0 main\
     >> /etc/apt/sources.list.d/llvm.list
wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
apt-get update && apt-get install -y --force-yes llvm-4.0