ignore warnings from boost headers when compiling with g++-9

src/ModelTree.cc

@@ -27,6 +27,8 @@
 #include "MinimumFeedbackSet.hh"
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wold-style-cast"
+#pragma GCC diagnostic ignored "-Wsign-compare"
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/graph/max_cardinality_matching.hpp>
 #include <boost/graph/strong_components.hpp>