Fix warnings reported by MSVS for shared library build

src/zone.h

Index: src/zone.h
diff --git a/src/zone.h b/src/zone.h
index 4dfd01d3589b93434fd18acbef2406381b452b31..f60ac0d3efc9363a6ecbbe1911d41a05b33fd6bc 100644
--- a/src/zone.h
+++ b/src/zone.h
@@ -152,6 +152,7 @@ class ZoneObject {
   // ZoneObjects should never be deleted individually; use
   // Zone::DeleteAll() to delete all zone objects in one go.
   void operator delete(void*, size_t) { UNREACHABLE(); }
+  void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); }
 };
 
 
@@ -197,6 +198,9 @@ class ZoneList: public List<T, ZoneListAllocationPolicy> {
       : List<T, ZoneListAllocationPolicy>(other.length()) {
     AddAll(other);
   }
+
+  void operator delete(void* pointer) { UNREACHABLE(); }
+  void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); }
 };