Add variables to support checking system manifest. am: c3d3a5e6f8 am: 70df5a377f am: 3366b4f836

Original change: https://android-review.googlesource.com/c/platform/system/libhidl/+/1461325

Change-Id: I43f53f25e921e48a03c81adbbe44f31f200d6292