src: fix startup snapshot reproducibility of InternalFieldInfo

`memset` before a placement `new` can be optimized away by GCC due to
lifetime analysis. This causes the buffer in the startup snapshot
vulnerable to ASLR.

Signed-off-by: Chengzhong Wu <cwu631@bloomberg.net>
PR-URL: #65684
Fixes: #65508
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Richard Lau <richard.lau@ibm.com>

Author: legendecas

src/node_snapshotable.h

@@ -44,8 +44,11 @@ struct InternalFieldInfoBase {
   template <std::derived_from<InternalFieldInfoBase> T>
   static T* New(EmbedderObjectType type) {
     void* buf = ::operator new[](sizeof(T));
-    memset(buf, 0, sizeof(T));  // Make the padding reproducible.
     T* result = new (buf) T;
+    // Zero the padding to make the bytes handed to V8 reproducible. Must come
+    // after the placement new, or -flifetime-dse drops it as a dead store.
+    // https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-fno-lifetime-dse
+    memset(static_cast<void*>(result), 0, sizeof(T));
     result->type = type;
     result->length = sizeof(T);
     return result;