Using unitypackage from https://developers.google.com/vr/unity/download

Steps to reproduce:
1. Create a new project, change platform to iOS or Android
2. Import the Unity VR SDK package from https://developers.google.com/vr/unity/download
3. Open Player Settings: notice Virtual Reality Supported is turned off
4. Build for iOS or Android
4. A message window appears saying "Please enable Cardboard in Player Settings > Virtual Reality Supported". Press Ok

Expected result: Build is not started. User is required to go and change settings as asked.
Actual result: Build proceeds.

Reproduced with: 2017.1.0b7, 5.6.1p1.
Not reproduced with: 5.5.3p3 (Player Settings > Virtual Reality Supported is not available in this version)