Sulogin: try to detect the real device(s) used for the system console

/dev/console if but only if /dev/console is used.  On Linux this can
be more than one device, e.g. a serial line as well as a virtual
console as well as a simple printer.

src/Makefile

@@ -105,7 +105,7 @@ utmpdump:	utmpdump.o
 runlevel:	runlevel.o
 
 sulogin:	LDLIBS += $(SULOGINLIBS) $(STATIC)
-sulogin:	sulogin.o
+sulogin:	sulogin.o consoles.o
 
 wall:		dowall.o wall.o