package management - Ubuntu 16.04: libclang 6 cannot be installed

I am currently trying to install doxygen, which has an unmet dependency libclang.so.6. I followed these instructions for installing this package, but it has its own dependencies.

The following packages have unmet dependencies:
clang-6.0 : Depends: libjsoncpp1 (>= 1.7.4) but 1.7.2-1 is to be installed
         Depends: libstdc++-7-dev but it is not installable
         Depends: libgcc-7-dev but it is not installable
         Depends: libobjc-7-dev but it is not installable
         Depends: libclang-common-6.0-dev (= 1:6.0.1~svn331815-1~exp1~20180509123840.80) but 1:6.0.1~svn331722-1~exp1~20180508135726.78 is to be installed
         Depends: libclang1-6.0 (= 1:6.0.1~svn331815-1~exp1~20180509123840.80) but 1:6.0.1~svn331722-1~exp1~20180508135726.78 is to be installed
E: Unable to correct problems, you have held broken packages.

I have tried installing each of these, both using apt-get and synaptic, but they all are either unavailable or not available in the correct version. How can I find and install the correct versions of each of these dependencies?