cmd: update to golang.org/x/sys@v0.18.0

cmd: update to golang.org/x/sys@v0.18.0

This is a requirement of x/telemetry so update it before updating
telemetry.

Commands run (in both std and cmd):
	go get golang.org/x/sys@v0.18.0
	go mod tidy
	go mod vendor

For #66099

Change-Id: I636f0c0be89c05b9213c461b1a2eb2a4afb8a84b
Reviewed-on: https://go-review.googlesource.com/c/go/+/569420
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Matloob <matloob@golang.org>