For all virtual targets for the same dependency graph as self,
            i.e. which belong to the same main target, add their directories
            to include path.

def adjust_properties (self, prop_set):
        """ For all virtual targets for the same dependency graph as self,
            i.e. which belong to the same main target, add their directories
            to include path.
        """
        assert isinstance(prop_set, property_set.PropertySet)
        s = self.targets () [0].creating_subvariant ()

        return prop_set.add_raw (s.implicit_includes ('include', 'H'))