Add clean targets removing jack and dex files

Those should help switching a tree from compiling with Jack back to
legacy toolchain.

Change-Id: I897a9a9923ed8147723b3ab6ad3f276e6b7094bf
diff --git a/core/cleanbuild.mk b/core/cleanbuild.mk
index cf980d8..58b1ee4 100644
--- a/core/cleanbuild.mk
+++ b/core/cleanbuild.mk
@@ -247,3 +247,17 @@
   $(info *** Done with the cleaning, now starting the real build.)
 endif
 force_installclean :=
+
+.PHONY: clean-jack-files
+clean-jack-files: clean-dex-files
+	$(hide) find $(OUT_DIR) -name "*.jack" | xargs rm -f
+	$(hide) find $(OUT_DIR) -type d -name "jack" | xargs rm -rf
+	@echo "All jack files have been removed."
+
+.PHONY: clean-dex-files
+clean-dex-files:
+	$(hide) find $(OUT_DIR) -name "*.dex" | xargs rm -f
+	$(hide) for i in `find $(OUT_DIR) -name "*.jar" -o -name "*.apk"` ; do ((unzip -l $$i 2> /dev/null | \
+				grep -q "\.dex$$" && rm -f $$i) || continue ) ; done
+	@echo "All dex files and archives containing dex files have been removed."
+