io_uring: support older versions of liburing
io_uring: support older versions of liburing

Summary: Some #if to support older versions of liburing as reported here; https://github.com/facebook/folly/issues/1832

Reviewed By: Orvid

Differential Revision: D38650359

fbshipit-source-id: eb78a7607eaaf151dc394cef72df3826c83fdfbc

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly