为什么在运行 `go get golang.org/x/tools/cmd/时没有创建二进制文件？

godoc并且gotour可以使用go build. gotour二进制文件创建时创建go get它的原因是什么，而godoc.

命令行输出：

[ user@pc:~/.gvm/pkgsets/go1.5.1/global ]

>> ls

[ user@pc:~/.gvm/pkgsets/go1.5.1/global ]

>> go env

GOARCH="amd64"

GOBIN=""

GOEXE=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOOS="linux"

GOPATH="/home/user/.gvm/pkgsets/go1.5.1/global"

GORACE=""

GOROOT="/home/user/.gvm/gos/go1.5.1"

GOTOOLDIR="/home/user/.gvm/gos/go1.5.1/pkg/tool/linux_amd64"

GO15VENDOREXPERIMENT=""

CC="gcc"

GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"

CXX="g++"

CGO_ENABLED="1"

[ user@pc:~/.gvm/pkgsets/go1.5.1/global ]

>> go get golang.org/x/tools/cmd/godoc

[ user@pc:~/.gvm/pkgsets/go1.5.1/global ]

>> ls

pkg  src

[ user@pc:~/.gvm/pkgsets/go1.5.1/global ]

>> go get golang.org/x/tour/gotour

[ user@pc:~/.gvm/pkgsets/go1.5.1/global ]

>> ls 

bin  pkg  src

[ user@pc:~/.gvm/pkgsets/go1.5.1/global ]

>> ls bin/

gotour

[ user@pc:~/.gvm/pkgsets/go1.5.1/global ]

>> cd src/golang.org/x/tools/cmd/godoc/

[ user@pc:~/.gvm/pkgsets/go1.5.1/global/src/golang.org/x/tools/cmd/godoc ]

>> go build

[ user@pc:~/.gvm/pkgsets/go1.5.1/global/src/golang.org/x/tools/cmd/godoc ]

>> ./godoc 

usage: godoc package [name ...]

    godoc -http=:6060

  -analysis string

        comma-separated list of analyses to perform (supported: type, pointer). See http://golang.org/lib/godoc/analysis/help.html

  -ex

        show examples in command line mode

  -goroot string

        Go root directory (default "/home/user/.gvm/gos/go1.5.1")

  -html

        print HTML in command-line mode

  -http string

        HTTP service address (e.g., ':6060')

  -httptest.serve string

        if non-empty, httptest.NewServer serves on this address and blocks

  -index

....