cppgc: Fix caged-heap-local-data.h for the test-include script

This wraps CagedHeapLocalData in #if defined(CPPGC_CAGED_HEAP)

Bug: v8:12231
Change-Id: I462ddbbde2308e8d786fb99d6a557c1dcaea8a4e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695586
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81038}

include/cppgc/internal/caged-heap-local-data.h

@@ -19,6 +19,8 @@
 #include <bit>
 #endif  // __cpp_lib_bitopts
 
+#if defined(CPPGC_CAGED_HEAP)
+
 namespace cppgc {
 namespace internal {
 
@@ -102,4 +104,6 @@ struct CagedHeapLocalData final {
 }  // namespace internal
 }  // namespace cppgc
 
+#endif  // defined(CPPGC_CAGED_HEAP)
+
 #endif  // INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_LOCAL_DATA_H_