VirtualMemoryCage related APIs need to be V8_EXPORT_PRIVATE

These are used by unittests which can be compiled as a separate binary
that links againt libv8.

Bug: chromium:1218005
Change-Id: Ibb29c4fa104be61fc26cbd6c1b349d74d74c50a6
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3202002
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77228}

src/init/vm-cage.h

@@ -42,7 +42,7 @@ namespace internal {
  * TODO(chromium:1218005) come up with a coherent naming scheme for this class
  * and the other "cages" in v8.
  */
-class V8VirtualMemoryCage {
+class V8_EXPORT_PRIVATE V8VirtualMemoryCage {
  public:
   // +-  ~~~  -+----------------------------------------  ~~~  -+-  ~~~  -+
   // |  32 GB  |                 (Ideally) 1 TB                 |  32 GB  |
@@ -109,7 +109,7 @@ class V8VirtualMemoryCage {
   std::unique_ptr<base::BoundedPageAllocator> cage_page_allocator_;
 };
 
-V8VirtualMemoryCage* GetProcessWideVirtualMemoryCage();
+V8_EXPORT_PRIVATE V8VirtualMemoryCage* GetProcessWideVirtualMemoryCage();
 
 #endif  // V8_VIRTUAL_MEMORY_CAGE