[dev.power64] cmd/9c: add Makefile

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://golang.org/cl/121370043

src/cmd/9c/Makefile

+# Copyright 2012 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.
+
+include ../../Make.dist