fix mingw x86_64 build

Author: xantares

src/cpp/flann/util/serialization.h

@@ -102,6 +102,7 @@ BASIC_TYPE_SERIALIZER(int);
 BASIC_TYPE_SERIALIZER(unsigned int);
 BASIC_TYPE_SERIALIZER(long);
 BASIC_TYPE_SERIALIZER(unsigned long);
+BASIC_TYPE_SERIALIZER(unsigned long long);
 BASIC_TYPE_SERIALIZER(float);
 BASIC_TYPE_SERIALIZER(double);
 BASIC_TYPE_SERIALIZER(bool);