fix a compile error

paddle/framework/tensor.h

@@ -37,8 +37,10 @@ class Tensor {
   template <typename T,  // must be POD types
             typename std::enable_if<std::is_pod<T>::value>::type* = nullptr>
   T* mutable_data(DDim dims, paddle::platform::Place place) {
-    if (holder_ == nullptr || holder_->Place() != place ||
-        holder_->Size() < product(dims) * sizeof(T)) {
+    if (holder_ == nullptr ||
+        !(holder_->Place() ==
+          place) /* some versions of boost::variant don't have operator!= */
+        || holder_->Size() < product(dims) * sizeof(T)) {
       holder_.reset(new PlaceholderImpl<T>(place, product(dims) * sizeof(T)));
     }
     return static_cast<T*>(holder_->Ptr());