Make it a fatal error if no source files for Java module.

Change-Id: Ia04158c11381b6b1687b9d5c699a9ea8ae3cb317
diff --git a/core/host_java_library.mk b/core/host_java_library.mk
index 5e35b90..ca27f28 100644
--- a/core/host_java_library.mk
+++ b/core/host_java_library.mk
@@ -23,6 +23,9 @@
 LOCAL_IS_HOST_MODULE := true
 LOCAL_BUILT_MODULE_STEM := javalib.jar
 
+# base_rules.mk looks at this
+all_res_assets :=
+
 ifeq ($(LOCAL_BUILD_HOST_DEX),true)
 ifneq ($(LOCAL_NO_STANDARD_LIBRARIES),true)
   LOCAL_JAVA_LIBRARIES := $(sort core-hostdex $(LOCAL_JAVA_LIBRARIES))