Add support for honggfuzz to BUILD_FUZZ_TEST

Change-Id: I38f70d1a57649635be95c59187da05ba22fcf687
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index 59297ea..5911f4c 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -93,6 +93,7 @@
 LOCAL_FULL_MANIFEST_FILE:=
 LOCAL_FULL_CLASSES_JACOCO_JAR:=
 LOCAL_FULL_CLASSES_PRE_JACOCO_JAR:=
+LOCAL_FUZZ_ENGINE:=
 LOCAL_GCNO_FILES:=
 LOCAL_GENERATED_SOURCES:=
 # Group static libraries with "-Wl,--start-group" and "-Wl,--end-group" when linking.