Add the ability to turn on proguard for java targets, and to call aapt
to generate a rules file for proguard for stuff from the manifest and
other resources that need to be kept.
diff --git a/core/config.mk b/core/config.mk
index 77239cd..37ca404 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -199,6 +199,7 @@
 TUNE2FS := tune2fs
 E2FSCK := e2fsck
 JARJAR := java -jar $(HOST_OUT_JAVA_LIBRARIES)/jarjar.jar
+PROGUARD := external/proguard/bin/proguard.sh
 
 # dx is java behind a shell script; no .exe necessary.
 DX := $(HOST_OUT_EXECUTABLES)/dx