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>

src/make.bash

@@ -66,6 +66,7 @@
 set -e
 
 export GOENV=off
+export GOWORK=off # Issue 51558
 unset GOBIN # Issue 14340
 unset GOFLAGS
 unset GO111MODULE

src/make.bat

@@ -47,6 +47,7 @@ setlocal
 :nolocal
 
 set GOENV=off
+set GOWORK=off
 set GOBUILDFAIL=0
 set GOFLAGS=
 set GO111MODULE=

src/make.rc

@@ -48,6 +48,7 @@ if(~ $1 -v) {
 }
 
 GOENV=off
+GOWORK=off
 GOFLAGS=()
 GO111MODULE=()
 GOROOT = `{cd .. && pwd}