cmd/go: fix autocgo test fail when set CGO_ENABLED during make.bash

Details see CL 706095

Fixes #75340

Change-Id: Ic7276f2fb3abc5f02f224d82e1f26844888f0a1e
Reviewed-on: https://go-review.googlesource.com/c/go/+/757182
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@google.com>

src/cmd/go/scriptconds_test.go

@@ -10,6 +10,7 @@ import (
 	"cmd/internal/script/scripttest"
 	"errors"
 	"fmt"
+	"internal/buildcfg"
 	"internal/testenv"
 	"os"
 	"os/exec"
@@ -47,6 +48,7 @@ func scriptConditions(t *testing.T) map[string]script.Cond {
 	add("git-sha256", script.OnceCondition("the local 'git' version is recent enough to support sha256 object/commit hashes", gitSupportsSHA256))
 	add("net", script.PrefixCondition("can connect to external network host <suffix>", hasNet))
 	add("trimpath", script.OnceCondition("test binary was built with -trimpath", isTrimpath))
+	add("default-cgo", lazyBool("when CGO_ENABLED=1|0 was set in make.bash", defaultCgo))
 
 	return conds
 }
@@ -194,3 +196,7 @@ func hasWorkingBzr() bool {
 	err = exec.Command(bzr, "help").Run()
 	return err == nil
 }
+
+func defaultCgo() bool {
+	return buildcfg.DefaultCGO_ENABLED == "1" || buildcfg.DefaultCGO_ENABLED == "0"
+}

src/cmd/go/testdata/script/README

@@ -391,6 +391,8 @@ The available conditions are:
 	runtime.Compiler == <suffix>
 [cross]
 	cmd/go GOOS/GOARCH != GOHOSTOS/GOHOSTARCH
+[default-cgo]
+	when CGO_ENABLED=1|0 was set in make.bash
 [exec:*]
 	<suffix> names an executable in the test binary's PATH
 [fuzz]

src/cmd/go/testdata/script/autocgo.txt

@@ -1,7 +1,7 @@
 # Test automatic setting of CGO_ENABLED based on $CC and what's in $PATH.
 
 [!cgo] skip
-[cross] skip
+[default-cgo] skip
 
 # Assume we're on a system that can enable cgo normally.
 env CGO_ENABLED=