dhcpcd-gtk: new glib causes deprecated warnings on old Gtk+

So just ignore them as this program is fixed to Gtk+2 and
the systray icon it uses will be removed entirely in Gtk+4.
As such a new implementation will need to be written.

src/dhcpcd-gtk/Makefile

@@ -15,6 +15,11 @@ CPPFLAGS+=	${NOTIFY} -I${TOPDIR}
 CFLAGS+=	${GTK_CFLAGS}
 LDADD+=		${LIB_DHCPCD} ${GTK_LIBS}
 
+# new glib causes deprecated warnings on old Gtk+.
+# A different Gtk+ front end needs to be written anyway as the systray
+# is gone in Gtk+4.
+CFLAGS+=	-Wno-deprecated-declarations
+
 .PHONY: dhcpcd-gtk
 
 include ../libdhcpcd/Makefile.inc