[sandbox] Use 64k block size on ppc64

Bug: v8:10391

Change-Id: Ib07287b166cfc54d4f52575ffecdc929f7ec3892
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3863406Reviewed-by: Samuel Groß <saelo@chromium.org>
Commit-Queue: Junliang Yan <junyan@redhat.com>
Cr-Commit-Position: refs/heads/main@{#82820}

src/sandbox/external-pointer-table.h

@@ -195,7 +195,12 @@ class V8_EXPORT_PRIVATE ExternalPointerTable {
 
   // An external pointer table grows and shrinks in blocks of this size. This
   // is also the initial size of the table.
+#if V8_TARGET_ARCH_PPC64
+  // PPC64 uses 64KB pages, and this must be a multiple of the page size.
+  static constexpr size_t kBlockSize = 64 * KB;
+#else
   static constexpr size_t kBlockSize = 16 * KB;
+#endif
   static constexpr size_t kEntriesPerBlock = kBlockSize / kSystemPointerSize;
 
   // When the table is swept, it first sets the freelist head to this special