test: make rundir match compiledir/errorcheckdir.

This allows test/dwarf to be supported by run.go.

Update #4139.

R=golang-dev, bradfitz, iant
CC=golang-dev
https://golang.org/cl/7064067

test/dwarf/dwarf.dir/main.go

@@ -0,0 +1,32 @@
+// $G $D/$F.go $D/z*.go && $L $F.$A && ./$A.out
+
+// NOTE: This test is not run by 'run.go' and so not run by all.bash.
+// To run this test you must use the ./run shell script.
+
+// Copyright 2009 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.
+
+package main
+func main() {
+F1()
+F2()
+F3()
+F4()
+F5()
+F6()
+F7()
+F8()
+F9()
+F10()
+F11()
+F12()
+F13()
+F14()
+F15()
+F16()
+F17()
+F18()
+F19()
+F20()
+}