win/clang: Fix a -Wmicrosoft-cast warning.

chrome/browser/safe_browsing/incident_reporting/verifier_test/verifier_test_dll.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Some pointless code that will become a DLL with some exports and relocs.
 
 #include <windows.h>
 
 namespace {
 
-void* g_somestate = nullptr;
+void (*g_somestate)(int) = nullptr;
 int g_somevalue = 0;
 
 }  // namespace
 
 extern "C"
 void DummyExport(int foo) {
   g_somevalue = foo;
 }
 
 extern "C"
 BOOL APIENTRY DllMain(HMODULE module, DWORD reason, LPVOID reserved) {
   if (reason == DLL_PROCESS_ATTACH)
     g_somestate = &DummyExport;
   else if (reason == DLL_PROCESS_DETACH)
     g_somestate = nullptr;
 
   return TRUE;
 }