In this version, Fortran support has been explicitely disabled (this is a temporary solution before we make sure that flang instead of dragonegg works correctly).
The current Dockerfile installs LLVM 3.4. Because this PR uses LLVM 7, the Dockerfile has to be modified to get LLVM 7 (notably for the CI to pass). This is probably best to do this before merging, the easiest way would probably be to download the binary releases from the LLVM website, since Ubuntu 14.04 doesn't have LLVM 7 packages.