Core: Fix build with old Qt

Qt's meta type system needs this include.

Change-Id: If465f65b142a952a0be1e440090186a5cb603c8b
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/coreplugin/systemsettings.cpp

@@ -9,6 +9,7 @@
 #include "dialogs/ioptionspage.h"
 #include "fileutils.h"
 #include "icore.h"
+#include "iversioncontrol.h" // sic!
 #include "vcsmanager.h"
 
 #include <utils/algorithm.h>