platform should be detected automatically

At Y-Gen Hackathon, the participant tried to mini-hacks for Android on his Windows platform. Then we spent long time to figure out that we should change platform to "windows".

It is ideal if build tool detects platform and automatically set appropriate platform.

Start by locating the build tool's platform-selection entry point and tracing how the current platform value is set. Reproduce the Windows setup described in the issue, then verify that an Android mini-hack selects the appropriate platform automatically without manual configuration.

Written by the indexing model from the issue text.