[gnome-control-center] thunderbolt: Fix build

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 9b32898ceee74647c08b2a0ea9a57cccd6136c2b
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Wed May 16 13:01:12 2018 -0500

    thunderbolt: Fix build
    
    Providing autocleanups for types you don't own is not a good idea, since
    it breaks when upstream adds those autocleanups.

 panels/thunderbolt/bolt-enums.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/panels/thunderbolt/bolt-enums.c b/panels/thunderbolt/bolt-enums.c
index de77737f8..bb34ba7c9 100644
--- a/panels/thunderbolt/bolt-enums.c
+++ b/panels/thunderbolt/bolt-enums.c
@@ -25,8 +25,10 @@
 
 #include <gio/gio.h>
 
+#if !GLIB_CHECK_VERSION(2, 57, 0)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (GEnumClass, g_type_class_unref);
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (GFlagsClass, g_type_class_unref);
+#endif
 
 gboolean
 bolt_enum_class_validate (GEnumClass *enum_class,