Add gatekeeper to userspace library build system am: e743222f7f am: 764d6b35d0 am: d0f1cd42cb am: 16d3b4f718

Original change: https://android-review.googlesource.com/c/platform/system/gatekeeper/+/1470590

Change-Id: Ifff1926a6e695c9d4cb0db62a6834977f1bef143