cmd/dist: enable external linking test for windows/amd64

Fixes #4069.

Change-Id: I2d2ea233f976aab3f356f9b508cdd246d5013e31
Signed-off-by: Shenghou Ma <minux@golang.org>
Reviewed-on: https://go-review.googlesource.com/7535
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/cmd/dist/test.go

@@ -351,7 +351,7 @@ func (t *tester) extLink() bool {
 		"linux-386", "linux-amd64", "linux-arm",
 		"netbsd-386", "netbsd-amd64",
 		"openbsd-386", "openbsd-amd64",
-		"windows-386":
+		"windows-386", "windows-amd64":
 		return true
 	case "darwin-386", "darwin-amd64":
 		// linkmode=external fails on OS X 10.6 and earlier == Darwin
@@ -370,10 +370,7 @@ func (t *tester) cgoTest() error {
 	env := mergeEnvLists([]string{"GOTRACEBACK=2"}, os.Environ())
 
 	iOS := t.goos == "darwin" && (t.goarch == "arm" || t.goarch == "arm64")
-	switch {
-	case t.goos == "windows" && t.goarch != "386":
-		fallthrough
-	case t.goos == "android", iOS:
+	if t.goos == "android" || iOS {
 		cmd := t.dirCmd("misc/cgo/test", "go", "test")
 		cmd.Env = env
 		return cmd.Run()
@@ -398,7 +395,7 @@ func (t *tester) cgoTest() error {
 			return err
 		}
 	case "darwin-386", "darwin-amd64",
-		"windows-386":
+		"windows-386", "windows-amd64":
 		if t.extLink() {
 			cmd := t.dirCmd("misc/cgo/test", "go", "test", "-ldflags", "-linkmode=external")
 			cmd.Env = env