build: add bootstrap.bash for bootstrapping new systems

Change-Id: Ic74830608fe077b4e97e8ce8009017c1e273c672
Reviewed-on: https://go-review.googlesource.com/6408Reviewed-by: Rob Pike <r@golang.org>

src/bootstrap.bash

+#!/bin/bash
+# Copyright 2015 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.
+
+# When run as (for example)
+#
+#	GOOS=linux GOARCH=ppc64 bootstrap.bash
+#
+# this script cross-compiles a toolchain for that GOOS/GOARCH
+# combination, leaving the resulting tree in ../../go-${GOOS}-${GOARCH}-bootstrap.
+# That tree can be copied to a machine of the given target type
+# and used as $GOROOT_BOOTSTRAP to bootstrap a local build.
+#
+# Only changes that have been committed to Git (at least locally,
+# not necessary reviewed and submitted to master) are included in the tree.
+
+set -e
+
+if [ "$GOOS" = "" -o "$GOARCH" = "" ]; then
+	echo "usage: GOOS=os GOARCH=arch ./bootstrap.bash" >&2
+	exit 2
+fi
+
+targ="../../go-${GOOS}-${GOARCH}-bootstrap"
+if [ -e $targ ]; then
+	echo "$targ already exists; remove before continuing"
+	exit 2
+fi
+
+unset GOROOT
+src=$(cd .. && pwd)
+echo "#### Copying to $targ"
+cp -R "$src" "$targ"
+cd "$targ"
+echo
+echo "#### Cleaning $targ"
+rm .gitignore
+git clean -f -d
+echo
+echo "#### Building $targ"
+echo
+cd src
+./make.bash --no-banner
+gohostos="$(../bin/go env GOHOSTOS)"
+gohostarch="$(../bin/go env GOHOSTARCH)"
+goos="$(../bin/go env GOOS)"
+goarch="$(../bin/go env GOARCH)"
+
+# NOTE: Cannot invoke go command after this point.
+# We're about to delete all but the cross-compiled binaries.
+cd ..
+if [ "$goos" = "$gohostos" -a "$goarch" = "$gohostarch" ]; then
+	# cross-compile for local system. nothing to copy.
+	# useful if you've bootstrapped yourself but want to
+	# prepare a clean toolchain for others.
+	true
+else
+	mv bin/*_*/* bin
+	rmdir bin/*_*
+	rm -rf "pkg/${gohostos}_${gohostarch}" "pkg/tool/${gohostos}_${gohostarch}"
+fi
+rm -rf pkg/bootstrap pkg/obj .git
+
+echo ----
+echo Bootstrap toolchain for "$GOOS/$GOARCH" installed in "$(pwd)".
+echo Building tbz.
+cd ..
+tar cf - "go-${GOOS}-${GOARCH}-bootstrap" | bzip2 -9 >"go-${GOOS}-${GOARCH}-bootstrap.tbz"
+ls -l "$(pwd)/go-${GOOS}-${GOARCH}-bootstrap.tbz"
+exit 0