Engage Jack incremental on demand

Each module may engage Jack incremental with

LOCAL_JACK_ENABLED := incremental

Include renaming of LOCAL_USE_JACK to LOCAL_JACK_ENABLED that is
now accepting 3 values "disabled", "full" and "incremental".

Change-Id: Icbff275b397bee36b29312e821f3e8d45f83fbcc
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 085b5fc..d6441bb 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -107,7 +107,7 @@
 LOCAL_ADDITIONAL_JAVA_DIR:=
 LOCAL_ALLOW_UNDEFINED_SYMBOLS:=
 LOCAL_DX_FLAGS:=
-LOCAL_USE_JACK:= $(ANDROID_COMPILE_WITH_JACK)
+LOCAL_JACK_ENABLED:=$(DEFAULT_JACK_ENABLED) # '' (ie disabled), disabled, full, incremental
 LOCAL_JACK_VM_ARGS := $(DEFAULT_JACK_VM_ARGS)
 LOCAL_JACK_EXTRA_ARGS := $(DEFAULT_JACK_EXTRA_ARGS)
 LOCAL_JACK_FLAGS:=