linux-user: pass correct host flags to eventfd2 call

This change makes conversion of TARGET_O_NONBLOCK and TARGET_O_CLOEXEC flags
to host flags before calling eventfd for TARGET_NR_eventfd2.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit 5947c697ce71898015ae1c6ac5d23d1ecc388552)
Typo, spelling and grammatical fixes

Minor fixes to documentation and code comments.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit e03ba136377ff0038276ba493473127338c68ebc)
[Patch] Fix against migration zero division segment fault