fix only shared variables could be declared as static in the device code

paddle/fluid/framework/dim.h

@@ -158,7 +158,13 @@ HOSTDEVICE int64_t& indexer<0>(Dim<0>& dim, int idx) {
 #else
   PADDLE_ASSERT(false);
 #endif
+#if (defined __CUDA_ARCH__) && (CUDA_VERSION < 8000)
+  // On CUDA versions previous to 8.0, only __shared__ variables
+  // could be declared as static in the device code.
+  int64_t head = 0;
+#else
   static int64_t head = 0;
+#endif
   return head;
 }
 
@@ -184,7 +190,13 @@ HOSTDEVICE int64_t indexer<0>(const Dim<0>& dim, int idx) {
 #else
   PADDLE_ASSERT(false);
 #endif
+#if (defined __CUDA_ARCH__) && (CUDA_VERSION < 8000)
+  // On CUDA versions previous to 8.0, only __shared__ variables
+  // could be declared as static in the device code.
+  int64_t head = 0;
+#else
   static int64_t head = 0;
+#endif
   return head;
 }