fix poolAllocator unordered_map bug on Mac OS X

* using map to replace unordered_map on Mac

Author: gangliao

paddle/math/PoolAllocator.h

@@ -19,6 +19,7 @@ limitations under the License. */
 #include <mutex>
 #include <vector>
 #include <unordered_map>
+#include <map>
 #include "Allocator.h"
 
 namespace paddle {
@@ -52,7 +53,11 @@ class PoolAllocator {
   void printAll();
   std::unique_ptr<Allocator> allocator_;
   std::mutex mutex_;
+#if defined(__APPLE__) || defined(__OSX__)
+  std::map<size_t, std::vector<void*>> pool_;
+#else
   std::unordered_map<size_t, std::vector<void*>> pool_;
+#endif
   size_t sizeLimit_;
   size_t poolMemorySize_;
   std::string name_;