msvcrt/tests: Correctly declare base class to avoid a compiler warning.

dlls/msvcrt/tests/cpp.c

@@ -969,7 +969,11 @@ static void test_rtti(void)
   void *child_class_sig0 = &child_class_sig0_vtbl[1];
   void *virtual_base_class_vtbl[2] = {&virtual_base_class_rtti.object_locator};
   int virtual_base_class_vbtbl[2] = {0, 0x100};
-  void *virtual_base_class[2] = {&virtual_base_class_vtbl[1], virtual_base_class_vbtbl};
+  struct {
+      void *virtual_base[2];
+      char data[0x110-sizeof(void*)];
+      void *vbthis;
+  } virtual_base_class = { {&virtual_base_class_vtbl[1], virtual_base_class_vbtbl} };
 
   static const char* e_name = "name";
   type_info *ti,*bti;
@@ -1082,7 +1086,7 @@ static void test_rtti(void)
   ok(casted == (char*)&child_class+4, "failed cast to child class (%p %p)\n", casted, &child_class);
 
   casted = p__RTDynamicCast(&virtual_base_class, 0, &virtual_base_class_rtti.type_info[0], &virtual_base_class_rtti.type_info[1], 0);
-  ok(casted == (char*)&virtual_base_class+0x110+sizeof(void*), "failed cast to child class (%p %p)\n", casted, &virtual_base_class);
+  ok(casted == &virtual_base_class.vbthis, "failed cast to child class (%p %p)\n", casted, &virtual_base_class);
 }
 
 struct _demangle {