builder: really set $GOBUILDEXIT for Windows

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5649074

misc/dashboard/builder/main.go

@@ -386,7 +386,7 @@ func (b *Builder) failBuild() bool {
 
 	log.Printf("fail %s %s\n", b.name, hash)
 
-	if err := b.recordResult(false, "", hash, "", "auto-fail mode run by " + os.Getenv("USER"), 0); err != nil {
+	if err := b.recordResult(false, "", hash, "", "auto-fail mode run by "+os.Getenv("USER"), 0); err != nil {
 		log.Print(err)
 	}
 	return true
@@ -478,7 +478,6 @@ func (b *Builder) envv() []string {
 		"GOOS=" + b.goos,
 		"GOARCH=" + b.goarch,
 		"GOROOT_FINAL=/usr/local/go",
-		"GOBUILDEXIT=1", // On Windows, exit all.bat with completion status.
 	}
 	for _, k := range extraEnv {
 		s, err := os.Getenverror(k)
@@ -497,6 +496,7 @@ func (b *Builder) envvWindows() []string {
 		"GOROOT_FINAL": "/c/go",
 		// TODO(brainman): remove once we find make that does not hang.
 		"MAKEFLAGS":   "-j1",
+		"GOBUILDEXIT": "1", // exit all.bat with completion status.
 	}
 	for _, name := range extraEnv {
 		s, err := os.Getenverror(name)