[libpeas] demo: fix build warning

[Christian Hergert <chergert src gnome org>]

commit d150c9dd65027aab82b2cae7507d073ef0414a47
Author: Christian Hergert <chergert redhat com>
Date:   Tue Feb 8 17:29:11 2022 -0800

    demo: fix build warning

 peas-demo/peas-demo.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/peas-demo/peas-demo.c b/peas-demo/peas-demo.c
index c6c0cf3f..fd9b766c 100644
--- a/peas-demo/peas-demo.c
+++ b/peas-demo/peas-demo.c
@@ -155,8 +155,10 @@ main (int    argc,
     peas_engine_add_search_path (engine, PEAS_BUILDDIR "/peas-demo/plugins", NULL);
   else
     {
+#ifdef G_OS_WIN32
       char *prefix;
       char *demo_pluginlibdir, *demo_plugindatadir;
+#endif
 
       peas_engine_add_search_path (engine,
                                    PEAS_LIBDIR "/peas-demo/plugins/",