src: add race.bash

Add race.bash so anyone with suitable hardware can run a race detector build. race.bash can be called from the dashboard builder by passing -cmd="race.bash".

Original source for race.bash is here, http://code.google.com/p/go-wiki/wiki/DashboardBuilders

TODO: add race.bat for windows/amd64

R=dvyukov, minux.ma, adg, rsc
CC=fullung, golang-dev
https://golang.org/cl/7179052

src/race.bash

+#!/usr/bin/env bash
+# Copyright 2013 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.
+
+# race.bash tests the standard library under the race detector.
+# http://golang.org/doc/articles/race_detector.html
+
+set -e
+
+function usage {
+	echo 'race detector is only supported on linux/amd64 and darwin/amd64' 1>&2
+	exit 1
+}
+
+case $(uname) in
+"Darwin")
+	# why Apple? why?
+	if sysctl machdep.cpu.extfeatures | grep -qv EM64T; then
+		usage
+	fi 
+	;;
+"Linux")
+	if [ $(uname -m) != "x86_64" ]; then
+		usage
+	fi
+	;;
+*)
+	usage
+	;;
+esac
+
+if [ ! -f make.bash ]; then
+	echo 'race.bash must be run from $GOROOT/src' 1>&2
+	exit 1
+fi
+. ./make.bash --no-banner
+go install -race std
+go test -race -short std
+go test -race -run=nothingplease -bench=.* -benchtime=.1s -cpu=4 std