Fix compilation with MinGW-w64.

src/platform-win32.cc

Index: src/platform-win32.cc
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index f16b5e74fda8705cd36db689eab1d2e94d0f0f17..dcfb679fd8687bcceb37c8e152b9416f2dbd9402 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -58,21 +58,26 @@ int localtime_s(tm* out_tm, const time_t* time) {
 }
 
 
-// Not sure this the correct interpretation of _mkgmtime
-time_t _mkgmtime(tm* timeptr) {
-  return mktime(timeptr);
-}
-
-
 int fopen_s(FILE** pFile, const char* filename, const char* mode) {
   *pFile = fopen(filename, mode);
   return *pFile != NULL ? 0 : 1;
 }
 
 
+#ifndef __MINGW64_VERSION_MAJOR
+
+// Not sure this the correct interpretation of _mkgmtime
+time_t _mkgmtime(tm* timeptr) {
+  return mktime(timeptr);
+}
+
+
 #define _TRUNCATE 0
 #define STRUNCATE 80
 
+#endif  // __MINGW64_VERSION_MAJOR
+
+
 int _vsnprintf_s(char* buffer, size_t sizeOfBuffer, size_t count,
                  const char* format, va_list argptr) {
   ASSERT(count == _TRUNCATE);