Add phony target javac-check.

javac-check covers all classes.jars that are compiled with javac
instead of jack. This target is required by tools that still need java
class files as input.

Bug: 26705771
Change-Id: I6896b9a6026a2a0dae6145d1ef5a839756aa3458
diff --git a/core/host_java_library.mk b/core/host_java_library.mk
index 9a13439..b5c5e9e 100644
--- a/core/host_java_library.mk
+++ b/core/host_java_library.mk
@@ -69,6 +69,8 @@
         $(LOCAL_ADDITIONAL_DEPENDENCIES)
 	$(transform-host-java-to-package)
 
+javac-check : $(full_classes_compiled_jar)
+
 # Run jarjar if necessary, otherwise just copy the file.
 ifneq ($(strip $(LOCAL_JARJAR_RULES)),)
 $(full_classes_jarjar_jar): PRIVATE_JARJAR_RULES := $(LOCAL_JARJAR_RULES)
@@ -105,4 +107,3 @@
 	@echo Copying: $@
 	$(hide) $(ACP) -fp $< $@
 endif # LOCAL_EMMA_INSTRUMENT
-