Allow proto builds to pass in java proto params.

Change-Id: I65fe0cd96f818f59267da6159e6bd2ad28f07a11
diff --git a/core/definitions.mk b/core/definitions.mk
index 7834baa..012dc44 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -892,7 +892,7 @@
 $(hide) for f in $(PRIVATE_PROTO_SRC_FILES); do \
         $(PROTOC) \
         $(addprefix --proto_path=, $(PRIVATE_PROTO_INCLUDES)) \
-        $(PRIVATE_PROTO_JAVA_OUTPUT_OPTION)=$(PRIVATE_PROTO_JAVA_OUTPUT_DIR) \
+        $(PRIVATE_PROTO_JAVA_OUTPUT_OPTION)="$(PRIVATE_PROTO_JAVA_OUTPUT_PARAMS):$(PRIVATE_PROTO_JAVA_OUTPUT_DIR)" \
         $(PRIVATE_PROTOC_FLAGS) \
         $$f || exit 33; \
         done