syscall: skip TestUseCgroupFD if cgroupfs not mounted
When building in schroot (for building Debian package),
the cgroupfs is not mounted in schroot (only sysfs is mounted).
Change-Id: Ieddac7b2f334d58d832f5d84d81af812badf3720
Reviewed-on: https://go-review.googlesource.com/c/go/+/460539
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com> Reviewed-by: Heschi Kreinick <heschi@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>