gtk: Fix compiler warning (GTK 3 deprecated function)

gtk: Fix compiler warning (GTK 3 deprecated function)

With GTK 3, the function gdk_cursor_unref is deprecated:

qemu/ui/gtk.c: In function ‘gd_cursor_define’:
qemu/ui/gtk.c:380:5: error:
 ‘gdk_cursor_unref’ is deprecated (declared at /usr/include/gtk-3.0/gdk/gdkcursor.h:233): Use 'g_object_unref' instead [-Werror=deprecated-declarations]

Fix the gcc compiler warning by using conditional compilation.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-id: 1371391987-10795-1-git-send-email-sw@weilnetz.de
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>