partially migrate coreutils to Config.src and Kbuild.src

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

coreutils/tr.c

@@ -18,6 +18,35 @@
 /* http://www.opengroup.org/onlinepubs/009695399/utilities/tr.html
  * TODO: graph, print
  */
+
+//kbuild:lib-$(CONFIG_TR) += tr.o
+
+//config:config TR
+//config:	bool "tr"
+//config:	default n
+//config:	help
+//config:	  tr is used to squeeze, and/or delete characters from standard
+//config:	  input, writing to standard output.
+
+config FEATURE_TR_CLASSES
+	bool "Enable character classes (such as [:upper:])"
+	default n
+	depends on TR
+	help
+	  Enable character classes, enabling commands such as:
+	  tr [:upper:] [:lower:] to convert input into lowercase.
+
+config FEATURE_TR_EQUIV
+	bool "Enable equivalence classes"
+	default n
+	depends on TR
+	help
+	  Enable equivalence classes, which essentially add the enclosed
+	  character to the current set. For instance, tr [=a=] xyz would
+	  replace all instances of 'a' with 'xyz'. This option is mainly
+	  useful for cases when no other way of expressing a character
+	  is possible.
+
 #include "libbb.h"
 
 enum {