base: Give more information when setting up asynchronous IO fails.

base: Give more information when setting up asynchronous IO fails.

When asynchronous IO fails, gem5 currently just says it failed and quits, and
doesn't give any more information about which step failed, or what
specifically about it failed.

This change adds two helpers which will attempt the fcntl, check for error
conditions, and in the event of a failure, include a message describing the
error code and what the arguments to fcntl were.

Change-Id: I316478172ab2aefd3788279dbc12744791385cd5
Reviewed-on: https://gem5-review.googlesource.com/4320
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>