kernel-symbol: respect ENABLE_POLKIT setting

This fixes the compilation when we have sysprofd fully disabled.
That is not an ideal configuration, but keeping it working
ensures that some of the code is easy copy/paste'able in the
future for some situations.

lib/symbols/sp-kernel-symbol.c

@@ -18,8 +18,13 @@
 
 #define G_LOG_DOMAIN "sp-kernel-symbol"
 
+#include "config.h"
+
 #include <gio/gio.h>
-#include <polkit/polkit.h>
+
+#ifdef ENABLE_POLKIT
+# include <polkit/polkit.h>
+#endif
 
 #include "sp-kallsyms.h"
 
@@ -87,6 +92,7 @@ type_is_ignored (guint8 type)
 static gboolean
 authorize_proxy (GDBusConnection *conn)
 {
+#ifdef ENABLE_POLKIT
   PolkitSubject *subject = NULL;
   GPermission *permission = NULL;
   const gchar *name;
@@ -113,6 +119,7 @@ authorize_proxy (GDBusConnection *conn)
 failure:
   g_clear_object (&subject);
   g_clear_object (&permission);
+#endif
 
   return FALSE;
 }