[llvm-dev] problem with apt.llvm.org?

[Andrew Kelley via llvm-dev]

This was working just a few hours ago, and now my CI server gives:

The following packages have unmet dependencies:
 clang-6.0 : Depends: libllvm6.0 (>= 1:6.0~svn298832-1~) but it is not going to be installed
             Depends: libstdc++6 (>= 4.9) but 4.8.4-2ubuntu1~14.04.4 is to be installed
             Depends: libstdc++-4.9-dev but it is not installable
             Depends: libgcc-4.9-dev but it is not installable
             Depends: libobjc-4.9-dev but it is not installable
             Depends: libclang-common-6.0-dev (= 1:6.0~svn326550-1~exp1~20180325230527.62) but it is not going to be installed
             Depends: libclang1-6.0 (= 1:6.0~svn326550-1~exp1~20180325230527.62) but it is not going to be installed
             Recommends: libomp-dev but it is not installable
 libclang-6.0-dev : Depends: libstdc++-4.9-dev but it is not installable
                    Depends: libgcc-4.9-dev but it is not installable
                    Depends: libobjc-4.9-dev but it is not installable
                    Depends: libclang1-6.0 (= 1:6.0~svn326550-1~exp1~20180325230527.62) but it is not going to be installed
                    Depends: libclang-common-6.0-dev (= 1:6.0~svn326550-1~exp1~20180325230527.62) but it is not going to be installed
 liblld-6.0 : Depends: libllvm6.0 (= 1:6.0~svn326550-1~exp1~20180325230527.62) but it is not going to be installed
 liblld-6.0-dev : Depends: lld-6.0 (= 1:6.0~svn326550-1~exp1~20180325230527.62) but it is not going to be installed
 llvm-6.0 : Depends: llvm-6.0-runtime (= 1:6.0~svn326550-1~exp1~20180325230527.62) but it is not going to be installed
            Depends: libllvm6.0 (>= 1:6.0~svn298832-1~) but it is not going to be installed
            Depends: libstdc++6 (>= 4.9) but 4.8.4-2ubuntu1~14.04.4 is to be installed
 llvm-6.0-dev : Depends: libllvm6.0 (= 1:6.0~svn326550-1~exp1~20180325230527.62) but it is not going to be installed
                Depends: libstdc++6 (>= 4.9) but 4.8.4-2ubuntu1~14.04.4 is to be installed
E: Unable to correct problems, you have held broken packages.

steps to reproduce:

sudo sh -c 'echo "deb http://apt.llvm.org/trusty/ llvm-toolchain-trusty-6.0 main" >> /etc/apt/sources.list'
wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
sudo apt-get update -q
sudo apt-get install -y clang-6.0 libclang-6.0 libclang-6.0-dev llvm-6.0 llvm-6.0-dev liblld-6.0 liblld-6.0-dev cmake wine1.6-amd64 s3cmd