vs2015: fix rename of _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 1671424942c9fae12fc560907c3d1d6ad357c1a1..2a4fe11622945abcfa5e265894a3dfa5a028920c 100644
--- a/sandbox/win/sandbox_poc/main_ui_window.cc
+++ b/sandbox/win/sandbox_poc/main_ui_window.cc
@@ -624,7 +624,11 @@ 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);

[Reid Kleckner, 2015/06/09 00:37:59]

Why not va_start from <stdarg.h>?

[scottmg, 2015/06/09 16:27:43]

No idea, it seemed strange enough that I left it alone, but I meant to ask too.

Justin, any reason that you know of?

[scottmg, 2015/06/09 16:28:28]

Hmm, attributed to one "initial.commit" so I'm guessing just random crazy
long-ago-sandbox-hacker. I'll switch it.

[scottmg, 2015/06/09 16:33:47]

and va_start is #defined to [_]_crt_va_start (as you probably already knew) so
seems silly. https://codereview.chromium.org/1168113007/

+#else
   _crt_va_start(arg_list, format);
+#endif
 
   wchar_t text[kMaxDebugBuffSize + 1];
   vswprintf_s(text, kMaxDebugBuffSize, format, arg_list);