fix destructor problem

test=develop

paddle/fluid/framework/trainer_factory.cc

@@ -22,6 +22,8 @@ limitations under the License. */
 namespace paddle {
 namespace framework {
 
+trainerMap g_trainer_map;
+
 std::string TrainerFactory::TrainerTypeList() {
   std::string trainer_types;
   for (auto iter = g_trainer_map.begin(); iter != g_trainer_map.end(); ++iter) {

paddle/fluid/framework/trainer_factory.h

@@ -22,7 +22,7 @@ namespace paddle {
 namespace framework {
 typedef std::shared_ptr<TrainerBase> (*CreatetrainerFunction)();
 typedef std::unordered_map<std::string, CreatetrainerFunction> trainerMap;
-trainerMap g_trainer_map;
+extern trainerMap g_trainer_map;
 
 #define REGISTER_TRAINER_CLASS(trainer_class)                   \
   namespace {                                                   \