grab sum from coreutils, clean it up, and make it busybox happy
diff --git a/coreutils/Makefile.in b/coreutils/Makefile.in
index 130bdf4..c9c42e0 100644
--- a/coreutils/Makefile.in
+++ b/coreutils/Makefile.in
@@ -71,6 +71,7 @@
 COREUTILS-$(CONFIG_SLEEP)   	+= sleep.o
 COREUTILS-$(CONFIG_SORT)    	+= sort.o
 COREUTILS-$(CONFIG_STTY)    	+= stty.o
+COREUTILS-$(CONFIG_SUM)     	+= sum.o
 COREUTILS-$(CONFIG_SYNC)    	+= sync.o
 COREUTILS-$(CONFIG_TAIL)    	+= tail.o
 COREUTILS-$(CONFIG_TEE)     	+= tee.o