Revert "Don't add a symlink for killall --- it's broken."

Looks like the previous revert of this commit (707204e) got dropped by
an `-s ours` merge.

This reverts commit c96e42498c99b179444e6812dd8b0583f0624fcd.
diff --git a/Android.mk b/Android.mk
index 21a91b9..9b1abef 100644
--- a/Android.mk
+++ b/Android.mk
@@ -279,6 +279,7 @@
     ionice \
     iorenice \
     kill \
+    killall \
     load_policy \
     ln \
     logname \