Fix Graphviz cmake module
This fixes the Graphviz cmake module, which now finds the LCG installation. I've no experience with cmake modules so I've mostly copied Gaudi's FindXrootd.cmake
. Please comment if this is better done differently.
Most notably this will allow to have the dot
executable in the runtime PATH
. I don't think we compile and link against the Graphviz anywhere.
This is expected to have no effect on the builds and tests.