Skip Proguard for EXPERIMENTAL_USE_OPENJDK9=true

Proguard doesn't support v53 class files. For now, this
CL simply replaces the Proguard step with a plain 'cp',
which is essentially a no-op.

To avoid apps exceeding the dex limit in this mode, this
CL also enables --multi-dex for those builds.

Test: Treehugger
Bug: 67673860
Change-Id: I17dc5d827360d606a0cac12e324f97e8dedbb630

core/java.mk

@@ -555,6 +555,10 @@ endif
 
 $(eval $(call copy-one-file,$(full_classes_jarjar_jar),$(full_classes_jar)))
 
+ifeq ($(EXPERIMENTAL_USE_OPENJDK9),true)
+LOCAL_DX_FLAGS := $(filter-out --multi-dex,$(LOCAL_DX_FLAGS)) --multi-dex
+endif
+
 my_desugaring :=
 ifndef LOCAL_IS_STATIC_JAVA_LIBRARY
 my_desugaring := true