Add watchOS support

This patch-set adds support for watchOS by building a minimal VLC with only audio playback capabilities of streams and local files. NFS, SMB, etc. support is disabled to optimize for size as well as many other third party libraries.

This proposes a minimal test app (in a separate file as diverges greatly from iOS) and xcodegen integration.

By using the new AVSampleBuffer aout, this port requires watchOS 7.5 or later with 8.0 for optimal performance.