[d8] Fix the shared-library build

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index bb85a7547a13786ef98747a975baee4d5103b898..81d65a4d52f43d47d882c3ceb94b785ef7ce40b7 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -2426,7 +2426,7 @@ class AllSpaces BASE_EMBEDDED {
 
 // Space iterator for iterating over all old spaces of the heap: Old space
 // and code space.  Returns each space in turn, and null when it is done.
-class OldSpaces BASE_EMBEDDED {
+class V8_EXPORT_PRIVATE OldSpaces BASE_EMBEDDED {
  public:
   explicit OldSpaces(Heap* heap) : heap_(heap), counter_(OLD_SPACE) {}
   OldSpace* next();