[release-branch.go1.25] runtime: don't negate eventfd errno

The Linux syscall package does this for us.

For #75337.
Fixes #77413.

Change-Id: I6a6a636c9bb5fe25fdc6f80dc8b538ebed60d00b
Reviewed-on: https://go-review.googlesource.com/c/go/+/701796
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
(cherry picked from commit d3be949ada01d7827f8edc87665fef5268634cb3)
Reviewed-on: https://go-review.googlesource.com/c/go/+/741223
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Florian Lehner <lehner.florian86@gmail.com>