func BuildInit() {
	if buildInitStarted {
		base.Fatalf("go: internal error: work.BuildInit called more than once")
	}
	buildInitStarted = true
	base.AtExit(closeBuilders)

	modload.Init()
	instrumentInit()
	buildModeInit()
	if err := fsys.Init(base.Cwd()); err != nil {
		base.Fatal(err)
	}

	// Make sure -pkgdir is absolute, because we run commands
	// in different directories.