cmd/nm: skip TestInternalLinkerCgoFile if no internal linking is supported

Fixes build.

Change-Id: I2fee624c8a4b228bb9f2889e241ea016a317bb11
Reviewed-on: https://go-review.googlesource.com/36373
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/cmd/nm/nm_cgo_test.go

@@ -7,13 +7,30 @@
 package main
 
 import (
+	"runtime"
 	"testing"
 )
 
 func TestInternalLinkerCgoFile(t *testing.T) {
+	if !canInternalLink() {
+		t.Skip("skipping; internal linking is not supported")
+	}
 	testGoFile(t, true, false)
 }
 
+func canInternalLink() bool {
+	switch runtime.GOOS {
+	case "dragonfly":
+		return false
+	case "linux":
+		switch runtime.GOARCH {
+		case "arm64", "mips64", "mips64le", "mips", "mipsle":
+			return false
+		}
+	}
+	return true
+}
+
 func TestExternalLinkerCgoFile(t *testing.T) {
 	testGoFile(t, true, true)
 }