Fix possibly wrong use of strncpy_s

This should also fix MinGW build.
Review URL: http://codereview.chromium.org/6376003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6382 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/platform-win32.cc

@@ -1474,7 +1474,7 @@ Thread::Thread(const char* name) : ThreadHandle(ThreadHandle::INVALID) {
 
 
 void Thread::set_name(const char* name) {
-  strncpy_s(name_, name, sizeof(name_));
+  OS::StrNCpy(Vector<char>(name_, sizeof(name_)), name, strlen(name));
   name_[sizeof(name_) - 1] = '\0';
 }