Make a metaprogramming hack more C++11-compatible

Source/wtf/MemoryInstrumentation.h

Index: Source/wtf/MemoryInstrumentation.h
diff --git a/Source/wtf/MemoryInstrumentation.h b/Source/wtf/MemoryInstrumentation.h
index a16982120d7c815139179327a4b46433e7f7e712..462bfb12d8cb24d65367e75c253b5fe0cbb2c896 100644
--- a/Source/wtf/MemoryInstrumentation.h
+++ b/Source/wtf/MemoryInstrumentation.h
@@ -138,7 +138,9 @@ private:
 #pragma warning(push)
 #pragma warning(disable: 4624) // Disable warning: destructor could not be generated because a base class destructor is inaccessible.
 #endif
-        struct Base : public Type, public BaseMixin { };
+        struct Base : public Type, public BaseMixin {
+          ~Base() {}
+        };
 #if COMPILER(MSVC)
 #pragma warning(pop)
 #endif