Add LOCAL_JAR_PROCESSOR

Allow using a host java library as an intermediate processor step
after javac but before desugar, proguard, or dx.

Test: manual
Change-Id: I7fb843e10d96c0167f6e4371582fabcc1454521f
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 0f38b80..a865597 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -115,6 +115,8 @@
 LOCAL_JARJAR_RULES:=
 LOCAL_JAR_MANIFEST:=
 LOCAL_JAR_PACKAGES:=
+LOCAL_JAR_PROCESSOR:=
+LOCAL_JAR_PROCESSOR_ARGS:=
 LOCAL_JAVACFLAGS:=
 LOCAL_JAVA_LANGUAGE_VERSION:=
 LOCAL_JAVA_LAYERS_FILE:=