windows: fix build on pre-Win10 systems

The use of DBG_PRINTEXCEPTION_WIDE_C was added for Win10 support,
but that define doesn't exist in older versions which means we fail
to build.  Put it behind an ifdef check to work everywhere.

Change-Id: Ibab8bddd5c19b4b50e356f59edeb3873c3104569
Reviewed-on: https://chromium-review.googlesource.com/441525
Reviewed-by: Mark Mentovai <mark@chromium.org>
diff --git a/src/client/windows/handler/exception_handler.cc b/src/client/windows/handler/exception_handler.cc
index fc22cd9..c42718c 100644
--- a/src/client/windows/handler/exception_handler.cc
+++ b/src/client/windows/handler/exception_handler.cc
@@ -47,6 +47,11 @@
   AppMemoryList::const_iterator end;
 } MinidumpCallbackContext;
 
+// This define is new to Windows 10.
+#ifndef DBG_PRINTEXCEPTION_WIDE_C
+#define DBG_PRINTEXCEPTION_WIDE_C ((DWORD)0x4001000A)
+#endif
+
 vector<ExceptionHandler*>* ExceptionHandler::handler_stack_ = NULL;
 LONG ExceptionHandler::handler_stack_index_ = 0;
 CRITICAL_SECTION ExceptionHandler::handler_stack_critical_section_;