Improved nothing-to-do-build

- Removed unnecessary dependency of
  "$(my_symlink) :  $(LOCAL_INSTALLED_MODULE)"
  We can generate symlink to nonexistent file.
  Actually in multilib build $(LOCAL_INSTALLED_MODULE) points to file
  that may not be the target file of the symlink and leads to always
  obsolete $(my_symlink) in the above dependnecy.
- Touch by-product in the dummy rule, to make sure the by-product is
  newer than the main-product.

Change-Id: I2f0e0cc197c49f920fa1f6794083b21cdc333c20
diff --git a/core/java.mk b/core/java.mk
index 6eb2247..1494c4b 100644
--- a/core/java.mk
+++ b/core/java.mk
@@ -611,13 +611,12 @@
 	@echo Building with Jack: $@
 	$(jack-java-to-dex)
 
-# The empty command was added because, without it, make misses the fact the $(built_dex) also
-# change $(full_classes_jack). Looks like it would test the date before running $(built_dex)
-# command.
+# $(full_classes_jack) is just by-product of $(built_dex_intermediate).
+# The dummy command was added because, without it, make misses the fact the $(built_dex) also
+# change $(full_classes_jack).
 $(full_classes_jack): $(built_dex_intermediate)
-	@echo
+	$(hide) touch $@
 
-# nothing to do it's built as a side effect of $(built_dex_intermediate)
 endif #LOCAL_IS_STATIC_JAVA_LIBRARY
 
 $(noshrob_classes_jack): PRIVATE_JACK_INTERMEDIATES_DIR := $(intermediates.COMMON)/jack-noshrob-rsc