test: convert tests to run.go whenever possible.

The other tests either need a complex procedure
or are architecture- or OS-dependent.

Update #4139.

R=golang-dev, daniel.morsing, iant
CC=golang-dev
https://golang.org/cl/6618062

test/ddd2.go

@@ -1,18 +1,9 @@
-// skip
+// rundir
 
 // Copyright 2010 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file is compiled and then imported by ddd3.go.
-
-package ddd
-
-func Sum(args ...int) int {
-	s := 0
-	for _, v := range args {
-		s += v
-	}
-	return s
-}
+// Test that variadic functions work across package boundaries.
 
+package ignored