internal/poll: handle (0, EINVAL) return from sendfile on Solaris
Also check for GOOS=illumos as well as GOOS=solaris.
Change-Id: I887e6cddc1b8ad0f4624c9491e089c6bb8bce70e
Reviewed-on: https://go-review.googlesource.com/c/go/+/622977
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>