Add support for AIO.

Packages describing “aio” as local USE flag

Package “aio” Flag Description
app-benchmarks/sysbench Add support for AIO.
app-emulation/qemu Enables support for Linux's Async IO
net-libs/libiio Enable asynchronous IO support
www-servers/nginx Enables file AIO support
dev-util/strace Enable dev-libs/libaio support for tracing Asynchronous I/O operations
sys-block/fio Enable AIO ioengine

All packages providing a “aio” USE flag (4)