Fix MinGW build

src/platform-win32.cc

Index: src/platform-win32.cc
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index c50424e57a44a83733c2078b70691a5a50689304..7791d62aa37bceca3f893e765a67c032104a9ceb 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -207,6 +207,12 @@ int strncpy_s(char* strDest, size_t numberOfElements,
   return 0;
 }
 
+
+inline void MemoryBarrier() {
+  int barrier = 0;
+  __asm__ __volatile__("xchgl %%eax,%0 ":"=r" (barrier));
+}
+
 #endif  // __MINGW32__
 
 // Generate a pseudo-random number in the range 0-2^31-1. Usually
@@ -858,13 +864,14 @@ void* OS::Allocate(const size_t requested,
 
   // VirtualAlloc rounds allocated size to page size automatically.
   size_t msize = RoundUp(requested, static_cast<int>(GetPageSize()));
-  intptr_t address = NULL;
+  intptr_t address = 0;
 
   // Windows XP SP2 allows Data Excution Prevention (DEP).
   int prot = is_executable ? PAGE_EXECUTE_READWRITE : PAGE_READWRITE;
 
   // For exectutable pages try and randomize the allocation address
-  if (prot == PAGE_EXECUTE_READWRITE && msize >= Page::kPageSize) {
+  if (prot == PAGE_EXECUTE_READWRITE &&
+      msize >= static_cast<size_t>(Page::kPageSize)) {
     address = (V8::RandomPrivate() << kPageSizeBits)
       | kAllocationRandomAddressMin;
     address &= kAllocationRandomAddressMax;
@@ -874,7 +881,7 @@ void* OS::Allocate(const size_t requested,
                               msize,
                               MEM_COMMIT | MEM_RESERVE,
                               prot);
-  if (mbase == NULL && address != NULL)
+  if (mbase == NULL && address != 0)
     mbase = VirtualAlloc(NULL, msize, MEM_COMMIT | MEM_RESERVE, prot);
 
   if (mbase == NULL) {
@@ -1347,6 +1354,7 @@ int OS::StackWalk(Vector<OS::StackFrame> frames) {
 
 #else  // __MINGW32__
 void OS::LogSharedLibraryAddresses() { }
+void OS::SignalCodeMovingGC() { }
 int OS::StackWalk(Vector<OS::StackFrame> frames) { return 0; }
 #endif  // __MINGW32__