Add killpg function

Change-Id:	I9bc347d264fe38faf2d0f9935d2ebb43a353196e
diff --git a/libc/Android.mk b/libc/Android.mk
index 229de77..0d3e2c3 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -26,6 +26,7 @@
 	unistd/initgroups.c \
 	unistd/isatty.c \
 	unistd/issetugid.c \
+	unistd/killpg.c \
 	unistd/lseek64.c \
 	unistd/mmap.c \
 	unistd/nice.c \