Invoke HIDL for C++ files

Change-Id: I917a04e92484f968b05b269bbaa2d458a7729b4c
(cherry picked from commit bbccdd6d152a37a03ece027b5896ddbc42db8a8b)
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index e271dd2..ff44320 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -107,6 +107,7 @@
 LOCAL_MANIFEST_INSTRUMENTATION_FOR:=
 LOCAL_AIDL_INCLUDES:=
 LOCAL_VTS_INCLUDES:=
+LOCAL_HIDL_INCLUDES:=
 LOCAL_JARJAR_RULES:=
 LOCAL_ADDITIONAL_JAVA_DIR:=
 LOCAL_ALLOW_UNDEFINED_SYMBOLS:=
@@ -144,6 +145,7 @@
 LOCAL_PROTOC_FLAGS:=
 LOCAL_PROTO_JAVA_OUTPUT_PARAMS:=
 LOCAL_VTSC_FLAGS:=
+LOCAL_HIDL_FLAGS:=
 LOCAL_NO_CRT:=
 LOCAL_NO_LIBGCC:=
 LOCAL_PROPRIETARY_MODULE:=