Clang 16 and GCC 14 do not allow implicit function declarations by default.
This adds the proper declaration.

Upstream PR: https://bugs.launchpad.net/gencfsm/+bug/2045767
Bug: https://bugs.gentoo.org/887207

Pascal Jäger <pascal.jaeger@leimstift.de> (2023-12-06)

--- a/src/tools.c
+++ b/src/tools.c
@@ -19,6 +19,17 @@
 
 #include "tools.h"
 
+#if !defined(VALA_EXTERN)
+#if defined(_MSC_VER)
+#define VALA_EXTERN __declspec(dllexport) extern
+#elif __GNUC__ >= 4
+#define VALA_EXTERN __attribute__((visibility("default"))) extern
+#else
+#define VALA_EXTERN extern
+#endif
+#endif
+VALA_EXTERN void gnome_encfs_manager_on_logout (void);
+
 gchar* get_glade_file(gchar *filename) {
     return g_build_filename(DATA_PATH, "glade", filename, NULL);
 }