Niall Douglas (s [underscore] sourceforge {at} nedprod [dot] com)
implement cmake hunter support.
Significantly slimmed down the headers being dragged in by the default LLFIO include, specifically that outcome<T> is no longer dragged in, and:
- #36 Async file i/o and storage profile have been modularised out of the default headers.
- #36 Mapped file i/o can be modularised out of the default headers.
Changed barrier kind to class enum, as per latest WG21 spec.
