misc/cgo/gmp: change pi.go to use standard Go copyright header

This file is not part of the benchmark shootout, and we wrote it, so use
the usual copyright header, not a partial version of the shootout
license.

Fixes #13575.

Change-Id: Ib610e2ad82914b4ef096a2424cfffe3383db2d5b
Reviewed-on: https://go-review.googlesource.com/17715
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

misc/cgo/gmp/pi.go

-// +build ignore
-
-/*
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are met:
-
-    * Redistributions of source code must retain the above copyright
-    notice, this list of conditions and the following disclaimer.
-
-    * Redistributions in binary form must reproduce the above copyright
-    notice, this list of conditions and the following disclaimer in the
-    documentation and/or other materials provided with the distribution.
+// 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.
 
-    * Neither the name of "The Computer Language Benchmarks Game" nor the
-    name of "The Computer Language Shootout Benchmarks" nor the names of
-    its contributors may be used to endorse or promote products derived
-    from this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
-AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
-ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
-LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
-CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
-SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
-INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
-CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
-ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-POSSIBILITY OF SUCH DAMAGE.
-*/
-
-/* The Computer Language Benchmarks Game
- * http://shootout.alioth.debian.org/
- *
- * contributed by The Go Authors.
- * based on pidigits.c (by Paolo Bonzini & Sean Bartlett,
- *                      modified by Michael Mellor)
- */
+// +build ignore
 
 package main