Support building with -Werror=strict-prototypes / -Werror=old-style-definition

Unfortunately "-std=c99" is not sufficient to make gcc ignore code that
uses constructs of earlier C standards, which were abandoned in C99.

See https://lwn.net/ml/fedora-devel/Y1kvF35WozzGBpc8@redhat.com/ for
some related discussion.

Change-Id: I84fd99442d0cc400fa562fa33623c142649230e2
diff --git a/src/vty/logging_vty.c b/src/vty/logging_vty.c
index c83dafd..59c8a9c 100644
--- a/src/vty/logging_vty.c
+++ b/src/vty/logging_vty.c
@@ -1196,7 +1196,7 @@
 
 /*! Register logging related commands to the VTY. Call this once from
  *  your application if you want to support those commands. */
-void logging_vty_add_cmds()
+void logging_vty_add_cmds(void)
 {
 	install_lib_element_ve(&enable_logging_cmd);
 	install_lib_element_ve(&disable_logging_cmd);