std,cmd: sync go.mod with new release branches

std,cmd: sync go.mod with new release branches

    cd src
    go get golang.org/x/sys@release-branch.go1.14-std
    go mod tidy && go mod vendor
    cd cmd
    go get golang.org/x/sys@release-branch.go1.14-cmd
    go get golang.org/x/tools@release-branch.go1.14
    go mod tidy && go mod vendor

Fixes #36851

Change-Id: Ib0a78eec90c92515b6f421972102cc8e8d0c08a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/217305
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>