Fix MinGW64 build.

src/platform-win32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 867 matching lines @@
 
   return base;
 }
 
 
 void* OS::Allocate(const size_t requested,
                    size_t* allocated,
                    bool is_executable) {
   // VirtualAlloc rounds allocated size to page size automatically.
   size_t msize = RoundUp(requested, static_cast<int>(GetPageSize()));
-  void* address = 0;
 
   // Windows XP SP2 allows Data Excution Prevention (DEP).
   int prot = is_executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
 
   LPVOID mbase = RandomizedVirtualAlloc(msize,
                                         MEM_COMMIT | MEM_RESERVE,
                                         prot);
 
   if (mbase == NULL) {
     LOG(ISOLATE, StringEvent("OS::Allocate", "VirtualAlloc failed"));
@@ skipping 1170 matching lines @@
 
 
 void Sampler::Stop() {
   ASSERT(IsActive());
   SamplerThread::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 
 } }  // namespace v8::internal