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

[sthagen]

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 golang#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

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