This fixes some warnings when compiling with Clang on Windows.

This change forces correct alignment of variables marked as atomic.

This includes a leading trimming node to act as a test.

This is hopefully a temporary measure to address a bug in the lock-free
algorithm.

Fixed compiling for iOS 11.x and earlier

Public issue https://github.com/mackron/miniaudio/issues/363

It looks like IOID will be null when both modes are supported.

Public issue https://github.com/mackron/miniaudio/issues/365