mingw: Remove annoying compilation warning.

Change the header inclusion order to avoid a very annoying compiler
warning with i586-mingw32msvc-gcc, which now uses more recent headers
and complains when winsock2.h is included after windows.h

Change-Id: Ie130e4181f94abae91827ecdf318bf082157f25f
diff --git a/qemu-os-win32.h b/qemu-os-win32.h
index ed2753d..5f032ea 100644
--- a/qemu-os-win32.h
+++ b/qemu-os-win32.h
@@ -26,8 +26,8 @@
 #ifndef QEMU_OS_WIN32_H
 #define QEMU_OS_WIN32_H
 
-#include <windows.h>
 #include <winsock2.h>
+#include <windows.h>
 
 /* Polling handling */