format_expr now outputs constants of type c_bit_field

This adds a case for outputting constants that have c_bit_field type as
numbers.

Author: kroening

src/util/format_expr.cpp

@@ -171,7 +171,9 @@ static std::ostream &format_rec(std::ostream &os, const constant_exprt &src)
     else
       return os << src.pretty();
   }
-  else if(type == ID_unsignedbv || type == ID_signedbv || type == ID_c_bool)
+  else if(
+    type == ID_unsignedbv || type == ID_signedbv || type == ID_c_bool ||
+    type == ID_c_bit_field)
     return os << *numeric_cast<mp_integer>(src);
   else if(type == ID_integer)
     return os << src.get_value();