Fix 6 extentedcommands declaration warnings

Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>

extendedcommands.c

@@ -641,8 +641,6 @@ int extendedcommand_file_exists()
     return 0 == stat(EXTENDEDCOMMAND_SCRIPT, &file_info);
 }
 
-void process_volumes();
-
 int edify_main(int argc, char** argv) {
     load_volume_table();
     process_volumes();

extendedcommands.h

@@ -47,3 +47,13 @@ void create_fstab();
 int has_datadata();
 
 void handle_failure(int ret);
+
+void process_volumes();
+
+int extendedcommand_file_exists();
+
+void show_install_update_menu();
+
+int confirm_selection(const char* title, const char* confirm);
+
+int run_and_remove_extendedcommand();