Accept an optional PACKAGING env parameter.

The parameter will indicate which directory contains intermediate
packages. For the ASAN builds, for example, this directory differs from
the default one.

Bug: 116020783
Test: m (on an affected ASAN build)
Change-Id: Ife35b6cf1f13c7db7e723f1b322a1f21d0231d72
diff --git a/tools/veridex/appcompat.sh b/tools/veridex/appcompat.sh
index 9a24d82..a24e84f 100755
--- a/tools/veridex/appcompat.sh
+++ b/tools/veridex/appcompat.sh
@@ -55,7 +55,9 @@
   OUT=${OUT_DIR}
 fi
 
-PACKAGING=${OUT}/target/common/obj/PACKAGING
+if [[ -z "${PACKAGING}" ]]; then
+  PACKAGING=${OUT}/target/common/obj/PACKAGING
+fi
 
 if [ -z "$ANDROID_HOST_OUT" ] ; then
   ANDROID_HOST_OUT=${OUT}/host/linux-x86