[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 d3be949ada)
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>

src/runtime/netpoll_epoll.go

@@ -27,7 +27,7 @@ func netpollinit() {
 	}
 	efd, errno := syscall.Eventfd(0, syscall.EFD_CLOEXEC|syscall.EFD_NONBLOCK)
 	if errno != 0 {
-		println("runtime: eventfd failed with", -errno)
+		println("runtime: eventfd failed with", errno)
 		throw("runtime: eventfd failed")
 	}
 	ev := syscall.EpollEvent{