OK, we are now using g++ to compile, using a sneaky option passed to
ocamlc through myocamlbuild.ml and extern "C".
OK, we spent a lot of time trying to get the C++ toString() function
to work, but ultimately it didn't. The UPPAAL library is messed up -
more precisely their C++ interface is, because at some point in the
process of conversion from a raw_t pointer to a dbm_t object, we find
the DBM ACTUALLY GETTING CHANGED, and that too in a way that MAKES
THEIR ASSERTIONS FAIL. So we decided to port the required function
over in a way that doesn't use the dbm_t class at all, and it works
now.