message: ci: add clang head/5.0 to CI image
diff: @@ -12,6 +12,11 @@ apt-get install -y gdb strace
  add-apt-repository -y ppa:ubuntu-toolchain-r/test
  apt-get update
  apt-get install -y g++-4.9
  +# clang head (currently 5.0)
  +wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
  +apt-add-repository "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial main"
  +apt-get update
  +apt-get install clang-5.0
  # Bazel and related dependencies.
  apt-get install -y openjdk-8-jdk curl
  echo "deb [arch=amd64] http://storage.googleapis.com/bazel-apt stable jdk1.8" | tee /etc/apt/sources.list.d/bazel.list
  