Android O seems to require Pipe to call the pipe2 system call.
But kernel version 2.6.23 only supports pipe, not pipe2.
So try pipe2 first, then fall back to pipe.

Fixes #30549

Change-Id: I3c5d86e8e945a5ec8a0ecea7853302952c0476c4
Reviewed-on: https://go-review.googlesource.com/c/go/+/165217
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>