Fix code generation exclusion

include/cppast/code_generator.hpp

@@ -193,7 +193,7 @@ namespace cppast
             /// the other functions have no effects.
             explicit operator bool() const noexcept
             {
-                return options_ != exclude;
+                return !options_.is_set(exclude);
             }
 
             /// \returns The generation options.

test/code_generator.cpp

@@ -157,7 +157,7 @@ struct foo{
             generation_options do_get_options(const cpp_entity& e) override
             {
                 if (e.name().front() == 'e')
-                    return code_generator::exclude;
+                    return code_generator::exclude | code_generator::declaration;
                 return {};
             }
         };