cmd/dlv: do not pass "linkmode internal" for windows on go1.9 and later

go1.9 no longer needs "linkmode internal" on windows.

Fixes #755
Fixes #477
Fixes #631

pkg/goversion/version_test.go

@@ -0,0 +1,52 @@
+package goversion
+
+import (
+	"runtime"
+	"testing"
+)
+
+func versionAfterOrEqual(t *testing.T, verStr string, ver GoVersion) {
+	pver, ok := Parse(verStr)
+	if !ok {
+		t.Fatalf("Could not parse version string <%s>", verStr)
+	}
+	if !pver.AfterOrEqual(ver) {
+		t.Fatalf("Version <%s> parsed as %v not after %v", verStr, pver, ver)
+	}
+	t.Logf("version string <%s> → %v", verStr, ver)
+}
+
+func TestParseVersionString(t *testing.T) {
+	versionAfterOrEqual(t, "go1.4", GoVersion{1, 4, 0, 0, 0, ""})
+	versionAfterOrEqual(t, "go1.5.0", GoVersion{1, 5, 0, 0, 0, ""})
+	versionAfterOrEqual(t, "go1.4.2", GoVersion{1, 4, 2, 0, 0, ""})
+	versionAfterOrEqual(t, "go1.5beta2", GoVersion{1, 5, -1, 2, 0, ""})
+	versionAfterOrEqual(t, "go1.5rc2", GoVersion{1, 5, -1, 0, 2, ""})
+	versionAfterOrEqual(t, "go1.6.1 (appengine-1.9.37)", GoVersion{1, 6, 1, 0, 0, ""})
+	versionAfterOrEqual(t, "go1.8.1.typealias", GoVersion{1, 6, 1, 0, 0, ""})
+	ver, ok := Parse("devel +17efbfc Tue Jul 28 17:39:19 2015 +0000 linux/amd64")
+	if !ok {
+		t.Fatalf("Could not parse devel version string")
+	}
+	if !ver.IsDevel() {
+		t.Fatalf("Devel version string not correctly recognized")
+	}
+}
+
+func TestInstalled(t *testing.T) {
+	installedVersion, ok := Installed()
+	if !ok {
+		t.Fatalf("could not parse output of go version")
+	}
+	runtimeVersion, ok := Parse(runtime.Version())
+	if !ok {
+		t.Fatalf("could not parse output of runtime.Version() %q", runtime.Version())
+	}
+
+	t.Logf("installed: %v", installedVersion)
+	t.Logf("runtime: %v", runtimeVersion)
+
+	if installedVersion != runtimeVersion {
+		t.Fatalf("version mismatch %#v %#v", installedVersion, runtimeVersion)
+	}
+}