apt-get update
+# Use newer packages from backports by default
+cat >/etc/apt/preferences <<EOF
+Package: *
+Pin: release a=stretch-backports
+Pin-Priority: 500
+EOF
+
+apt-get dist-upgrade -y
+
apt-get install -y --no-remove \
llvm-3.9-dev \
libclang-3.9-dev \