partially migrate coreutils to Config.src and Kbuild.src

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

coreutils/cat.c

@@ -10,6 +10,18 @@
 /* BB_AUDIT SUSv3 compliant */
 /* http://www.opengroup.org/onlinepubs/007904975/utilities/cat.html */
 
+//kbuild:lib-$(CONFIG_CAT)     += cat.o
+//kbuild:lib-$(CONFIG_MORE)    += cat.o # more uses it if stdout isn't a tty
+//kbuild:lib-$(CONFIG_LESS)    += cat.o # less too
+//kbuild:lib-$(CONFIG_CRONTAB) += cat.o # crontab -l
+
+//config:config CAT
+//config:	bool "cat"
+//config:	default n
+//config:	help
+//config:	  cat is used to concatenate files and print them to the standard
+//config:	  output. Enable this option if you wish to enable the 'cat' utility.
+
 #include "libbb.h"
 
 /* This is a NOFORK applet. Be very careful! */