Be explicit about use of W version on Windows.

runtime/bin/process_win.cc

Index: runtime/bin/process_win.cc
diff --git a/runtime/bin/process_win.cc b/runtime/bin/process_win.cc
index 6a400ac6f5009ba72e33e12152dc6bc2934c80ad..a0737175f2230ca3b8e1e8cb976112193958e5ec 100644
--- a/runtime/bin/process_win.cc
+++ b/runtime/bin/process_win.cc
@@ -338,7 +338,7 @@ static DeleteProcThreadAttrListFn delete_proc_thread_attr_list = NULL;
 static bool EnsureInitialized() {
   static bool load_attempted = false;
   static dart::Mutex mutex;
-  HMODULE kernel32_module = GetModuleHandle(L"kernel32.dll");
+  HMODULE kernel32_module = GetModuleHandleW(L"kernel32.dll");
   if (!load_attempted) {
     MutexLocker locker(&mutex);
     if (load_attempted) return delete_proc_thread_attr_list != NULL;