default:
		t.Fatalf("bad case %d", test)
	}

	cmd := testenv.Command(t, testenv.GoToolPath(t), "build")
	cmd.Dir = dir
	cgoCflags += " -flto"
	cmd.Env = append(cmd.Environ(), "CGO_CFLAGS="+cgoCflags)

	t.Logf("CGO_CFLAGS=%q %v", cgoCflags, cmd)
	out, err := cmd.CombinedOutput()
	t.Logf("%s", out)

	if err != nil {
		t.Logf("go build failed: %v", err)

# Other flags are added if CGO_ENABLED is true.
env CGO_ENABLED=0
go build
go version -m m$GOEXE
stdout '^\tbuild\tCGO_ENABLED=0$'
! stdout CGO_CPPFLAGS|CGO_CFLAGS|CGO_CXXFLAGS|CGO_LDFLAGS

[cgo] env CGO_ENABLED=1
[cgo] env CGO_CPPFLAGS=-DFROM_CPPFLAGS=1
[cgo] env CGO_CFLAGS=-DFROM_CFLAGS=1
[cgo] env CGO_CXXFLAGS=-DFROM_CXXFLAGS=1
[cgo] env CGO_LDFLAGS=-L/extra/dir/does/not/exist

// of the Go command.
const KnownEnv = `
	AR
	CC
	CGO_CFLAGS
	CGO_CFLAGS_ALLOW
	CGO_CFLAGS_DISALLOW
	CGO_CPPFLAGS
	CGO_CPPFLAGS_ALLOW
	CGO_CPPFLAGS_DISALLOW
	CGO_CXXFLAGS
	CGO_CXXFLAGS_ALLOW
	CGO_CXXFLAGS_DISALLOW
	CGO_ENABLED
	CGO_FFLAGS
	CGO_FFLAGS_ALLOW
	CGO_FFLAGS_DISALLOW
	CGO_LDFLAGS
	CGO_LDFLAGS_ALLOW
	CGO_LDFLAGS_DISALLOW
	CXX
	FC

        GCCGO="gccgo"
        AR="ar"
        CC="clang"
        CXX="clang++"
        CGO_ENABLED="1"
        GOMOD="/dev/null"
        GOWORK=""
        CGO_CFLAGS="-O2 -g"
        CGO_CPPFLAGS=""
        CGO_CXXFLAGS="-O2 -g"
        CGO_FFLAGS="-O2 -g"
        CGO_LDFLAGS="-O2 -g"
        PKG_CONFIG="pkg-config"

		if err != nil {
			t.Fatalf("%v: %v\n%s", cmd, err, cmd.Stderr)
		}
		out := string(bytes.TrimSpace(line))
		t.Logf("%v: %q", cmd, out)
		return out
	}

	cc := goEnv("CC")
	cgoCflags := goEnv("CGO_CFLAGS")

	t.Parallel()

	tmpdir := t.TempDir()
	dllfile := filepath.Join(tmpdir, "test.dll")
	exefile := filepath.Join(tmpdir, "gotest.exe")

	// build go dll

env CGO_CFLAGS=-fplugin
go build -x -n -o dummy.exe ./usesInternalCgo
stderr preferlinkext
env CGO_CFLAGS=-fprofile-instr-generate
go build -x -n -o dummy.exe ./usesInternalCgo
stderr preferlinkext

# The -fdebug-prefix-map=path is permitted for internal linking.
env CGO_CFLAGS=-fdebug-prefix-map=/some/sandbox/execroot/workspace=/tmp/new
go build -x -n -o dummy.exe ./usesInternalCgo
! stderr preferlinkext

env GOSUMDB=nodefault
env GOPROXY=nodefault
env GO111MODULE=auto
env CGO_CFLAGS=nodefault
env CGO_CPPFLAGS=nodefault

go env -changed
# linux output like GOTOOLCHAIN='local'
# windows output like GOTOOLCHAIN=local
stdout 'GOTOOLCHAIN=''?local''?'
stdout 'GOSUMDB=''?nodefault''?'
stdout 'GOPROXY=''?nodefault''?'
stdout 'GO111MODULE=''?auto''?'
stdout 'CGO_CFLAGS=''?nodefault''?'
stdout 'CGO_CPPFLAGS=''?nodefault''?'

# golang.org/issue/46347: a stale runtime/cgo should only force a single rebuild

[!cgo] skip
[short] skip


# If we set a unique CGO_CFLAGS, the installed copy of runtime/cgo
# should be reported as stale.

env CGO_CFLAGS=-DTestScript_cgo_stale=true
stale runtime/cgo


# If we then build a package that uses cgo, runtime/cgo should be rebuilt and
# cached with the new flag, but not installed to GOROOT.

# Explicitly rebuild it to ensure that it is cached.
# (See https://go.dev/issue/50892.)
#
# If running in non-short mode, explicitly vary CGO_CFLAGS
# as a control case (to ensure that our regexps do catch rebuilds).

[!short] env GOCACHE=$WORK/cache
[!short] env CGO_CFLAGS=-DTestScript_cgo_stale_precompiled=true
go build -x runtime/cgo
[!short] stderr '[/\\]cgo'$GOEXE'["]? .* -importpath runtime/cgo'

		}
		args = append(args, strings.Fields(string(out))...)
	}
	args = append(args, "-I", tmpdir)
	args = append(args, strings.Fields(os.Getenv("CGO_CFLAGS"))...)
	args = append(args, bp.CgoCFLAGS...)
	args = append(args, bp.CgoFiles...)

	cmd := exec.Command(args[0], args[1:]...)
	cmd.Dir = bp.Dir
	if err := cmd.Run(); err != nil {
		return nil, fmt.Errorf("go tool cgo: %w", err)