cmd: update github.com/google/pprof dependencies

cmd: update github.com/google/pprof dependencies

Spun out of CL 626397, this change vendors in the latest
github.com/google/pprof and that also required updating
golang.org/x/sys to v0.27.

Change-Id: I72ee514494a9e7c36a8943d78f15bdd0445c5cd5
Reviewed-on: https://go-review.googlesource.com/c/go/+/626995
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>