Generate graphivz/dot dependencies for custom target
Currently when we ask CMake to dump the graphviz/dot file of targets dependencies we "only" get dependencies for a subset of targets types namelly: executable, static-shared-module library and interface library. Custom Target are excluded: see: https://gitlab.kitware.com/cmake/cmake/blob/v3.11.1/Source/cmGraphVizWriter.cxx#L572
I would be nice if could have ALL targets in the graph so that one can work on the "whole dep graph".