use va_start, not [_]_crt_va_start

sandbox/win/sandbox_poc/main_ui_window.cc

Index: sandbox/win/sandbox_poc/main_ui_window.cc
diff --git a/sandbox/win/sandbox_poc/main_ui_window.cc b/sandbox/win/sandbox_poc/main_ui_window.cc
index 2a4fe11622945abcfa5e265894a3dfa5a028920c..6c5d17727a0d8d94ee14eff7e4c421d57f456143 100644
--- a/sandbox/win/sandbox_poc/main_ui_window.cc
+++ b/sandbox/win/sandbox_poc/main_ui_window.cc
@@ -5,6 +5,7 @@
 #include <windows.h>
 #include <CommCtrl.h>
 #include <commdlg.h>
+#include <stdarg.h>
 #include <time.h>
 #include <windowsx.h>
 #include <atlbase.h>
@@ -624,11 +625,7 @@ void MainUIWindow::AddDebugMessage(const wchar_t* format, ...) {
   const int kMaxDebugBuffSize = 1024;
 
   va_list arg_list;
-#if _MSC_VER >= 1900
-  __crt_va_start(arg_list, format);
-#else
-  _crt_va_start(arg_list, format);
-#endif
+  va_start(arg_list, format);
 
   wchar_t text[kMaxDebugBuffSize + 1];
   vswprintf_s(text, kMaxDebugBuffSize, format, arg_list);