[gtk+] gdkscreen-win32.c: Also define _WIN32_WINNT

[Chun-wei Fan <fanchunwei src gnome org>]

commit fcd216a409232b9e29cb6ebfb15b9e01edca2078
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Fri Nov 11 21:03:46 2016 +0800

    gdkscreen-win32.c: Also define _WIN32_WINNT
    
    As in the last commit on gdkdisplay-win32.c, we need to define that to be
    0x0600 (Vista) or later so that the items needed in the Windows headers be
    activated.
    
    See: https://bugzilla.gnome.org/show_bug.cgi?id=768081#c62

 gdk/win32/gdkscreen-win32.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/gdk/win32/gdkscreen-win32.c b/gdk/win32/gdkscreen-win32.c
index 47f0168..63a6cf7 100644
--- a/gdk/win32/gdkscreen-win32.c
+++ b/gdk/win32/gdkscreen-win32.c
@@ -16,6 +16,9 @@
  */
 
 #include "config.h"
+
+#define _WIN32_WINNT 0x0600
+
 #include "gdk.h"
 #include "gdkprivate-win32.h"
 #include "gdkscreenprivate.h"