unix: check Faccessat2 returning EPERM in Faccessat
unix: check Faccessat2 returning EPERM in Faccessat

Some systems (e.g. the linux-arm and linux-arm64-packet builders) return
EPERM instead of ENOSYS on unimplemented syscalls. Fall back to the
existing glibc-like implementation in Faccessat in this case as well.

This fixes tests on the linux-arm and linux-arm64-packet builders after
CL 246537.

Change-Id: I7d7598f9694a2db19bd17e79f333d5de3a31c6e2
Reviewed-on: https://go-review.googlesource.com/c/sys/+/246817
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

multiplay/golang-sys,golang/sys,multiplay/golang-sys,golang/sys,multiplay/golang-sys,golang/sys,multiplay/golang-sys