build: force GOWORK=off in make.{bash,bat,rc}

build: force GOWORK=off in make.{bash,bat,rc}

While building Go from source, workspace mode should be disabled,
even if the external environment tries to configure it otherwise.

Fixes #51558.

Change-Id: Icd7577860271f59a8f94406214b111280e4b65b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/393879
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>