Macro nros_platform_export_threading 

macro_rules! nros_platform_export_threading {
    ($ty:ty) => { ... };
}

Emit nros_platform_task_*, nros_platform_mutex_*, nros_platform_mutex_rec_*, and nros_platform_condvar_* delegating to <$ty as PlatformThreading>. Skip this macro on platforms without kernel threads.