Enable .toc optimization for SDK stub

As we don't build .dex file for SDK stub, use .jar.toc even for
the .jack file. This should be safe we are building the .jack
file from .jar file.

This was actually necessary to achieve performance improvement
mentioned in https://android-review.googlesource.com/#/c/186470/

Bug: 24597504
Change-Id: I7d4518421b64510ce83229d9f19a654888753a84

build/build_android_stubs.mk

@@ -57,8 +57,9 @@ $(jack_lib) : $(full_target) $(JILL_JAR) $(JACK)
 
 $(call define-jar-to-toc-rule, $(full_target))
 
-# As we don't have .dex file for the SDK stub, we cannot use .toc
-# optimization for it. We update the timestamp of .toc file whenever
-# .jack is updated so dependents will be always rebuilt.
-$(dex_toc): $(jack_lib)
-	touch $@
+# As we don't have .dex file for the SDK stub, we cannot generate .toc
+# file from .dex file. Use .toc file generated from .jar instead.
+$(dex_toc): $(full_target).toc $(jack_lib)
+	$(hide) cp $< $@.tmp
+	$(call commit-change-for-toc, $@)
+.KATI_RESTAT: $(dex_toc)