Added missing include directives.

diff --git a/include/objbase.h b/include/objbase.h
index 52c04ab..a6d3312 100644
--- a/include/objbase.h
+++ b/include/objbase.h
@@ -6,6 +6,7 @@
 #include "unknwn.h"
 
 /* the following depend only on obj_base.h */
+#include "wine/obj_base.h"
 #include "wine/obj_misc.h"
 #include "wine/obj_channel.h"
 #include "wine/obj_clientserver.h"