[release-branch.go1.10] runtime: use Android O friendly syscalls on 64-bit machines

Android O disallows open on 64-bit, so let's use openat with AT_FDCWD to
achieve the same behavior.

Android O disallows epoll_wait on 64-bit, so let's use epoll_pwait with
the last argument as NULL to achieve the same behavior.

See here:
https://android.googlesource.com/platform/bionic/+/master/libc/seccomp/arm64_app_policy.cpp
https://android.googlesource.com/platform/bionic/+/master/libc/seccomp/mips64_app_policy.cpp
https://android.googlesource.com/platform/bionic/+/master/libc/seccomp/x86_64_app_policy.cpp

Fixes #23750

Change-Id: If8d5a663357471e5d2c1f516151344a9d05b188a
Reviewed-on: https://go-review.googlesource.com/92895


Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-on: https://go-review.googlesource.com/102792
Run-TryBot: Andrew Bonventre <andybons@golang.org>