cmd/go: allow to install cross-compiled binaries when GOBIN is set

[hyangah]

$ GOBIN=/tmp/release GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go1.20rc1 install golang.org/dl/go1.19.4@latest
go: cannot install cross-compiled binaries when GOBIN is set

What version of Go are you using (go version)?

$ go version
go version go1.19.4 darwin/amd64

What did you do?

Want to build a go tool for a different platform, but want the compiled binary to be in a directory different from my default installation directory.

What did you expect to see?

Successfully cross-compile the binary and have the result somewhere under GOBIN.

What did you see instead?

Error.

I believe the rejection of cross-compiled binary when GOBIN is set has a long history, that predates both Go modules and the recent major change in the meaning of go install <main_package_path>@<version> repurposed for clean tool installation. There were multiple related discussion topics (#13063 #14295 #9769) but all were closed as "FrozenDueToAge".

An alternative is to support -o flag for go install or go build <main_package>@<version> which is under discussion in a different context. #44469.

[dmitshur]

CC @bcmills, @matloob.

[bcmills]

We had some confusion around the semantics of GOBIN circa Go 1.13 that resulted in a bit of a shift, which seems to have stuck.

I agree that, given the current semantics (and especially given the current interop stories around CPU migrations on various vendors), it seems fine to allow go install to install cross-compiled binaries to GOBIN.