Fixed compilation warnings & errors on iOS

This applies for resource manager data source and sounds.

This addresses an issue where data streams can have a delay between
loop points due to it's asynchronous loading mechanism. With this
change, streams should now have a clean loop transition.

This is used for giving the data source a hint as to whether or not
it'll be used in a looping situations. It's required for some data
sources which need to know about it's looping state for caching or
whatnot.

The API for the resource management part of this commit may change.

Public issue https://github.com/mackron/miniaudio/issues/355