heap: fix endianness issue with PopulateEmbedderDataSnapshot

Need to reverse the index on big endian platforms due to
this previous change: https://crrev.com/c/1508572

Change-Id: I12e0230d929f5f16ecd2300a49970f92b0d3be50
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3402363Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Milad Farazmand <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/main@{#78699}

src/objects/embedder-data-slot-inl.h

@@ -207,11 +207,17 @@ void EmbedderDataSlot::PopulateEmbedderDataSnapshot(
   const Address field_base =
       FIELD_ADDR(js_object, js_object.GetEmbedderFieldOffset(entry_index));
 
-  reinterpret_cast<AtomicTagged_t*>(&snapshot)[0] =
+#if defined(V8_TARGET_BIG_ENDIAN) && defined(V8_COMPRESS_POINTERS)
+  const int index = 1;
+#else
+  const int index = 0;
+#endif
+
+  reinterpret_cast<AtomicTagged_t*>(&snapshot)[index] =
       AsAtomicTagged::Relaxed_Load(
           reinterpret_cast<AtomicTagged_t*>(field_base + kTaggedPayloadOffset));
 #ifdef V8_COMPRESS_POINTERS
-  reinterpret_cast<AtomicTagged_t*>(&snapshot)[1] =
+  reinterpret_cast<AtomicTagged_t*>(&snapshot)[1 - index] =
       AsAtomicTagged::Relaxed_Load(
           reinterpret_cast<AtomicTagged_t*>(field_base + kRawPayloadOffset));
 #endif  // V8_COMPRESS_POINTERS