build/env: add cross compile toolchain for armhf

Moved arm to armel, if anyone wants that in the future.

Change-Id: I57db5c8dff12c02cd2ceb4bd657d5fa63040985c
Reviewed-on: https://go-review.googlesource.com/29684
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

env/crosscompile/linux-armel-stretch/README

@@ -1,2 +1,2 @@
 The docker image created from this directory can be used to cross compile go
-from linux/amd64 to linux/arm.
+from linux/amd64 to linux/armel.

env/crosscompile/linux-armhf-stretch/Dockerfile

@@ -0,0 +1,53 @@
+# Copyright 2016 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.
+
+# Linux builder VM running Debian stretch (i.e. Debian testing)
+# Docker tag gobuilders/linux-armhf-stretch
+
+FROM debian:stretch
+MAINTAINER golang-dev <golang-dev@googlegroups.com>
+
+ENV DEBIAN_FRONTEND noninteractive
+
+# curl: for getting and unpacking Go 1.4 source
+# git-core: for interacting with the Go source & subrepos
+# gcc, libc-dev: for building Go's bootstrap 'dist' prog
+# gcc-armhf-linux-gnu, libc6-dev-armhf-cross: for armhf builds
+# linux-libc-dev(armhf): for asm/errno.h
+# procps, lsof, psmisc: misc tools
+RUN dpkg --add-architecture armhf \
+	&& apt-get update && apt-get install -y \
+	bzip2 \
+	ca-certificates \
+	curl \
+	git-core \
+	gcc \
+	libc6-dev \
+	gcc-arm-linux-gnueabihf \
+	libc6-dev-armhf-cross \
+	linux-libc-dev:armhf \
+	procps \
+	lsof \
+	psmisc \
+	--no-install-recommends \
+	&& rm -rf /var/lib/apt/lists/*
+
+RUN mkdir -p /go1.4-amd64 \
+	&& ( \
+		curl --silent https://storage.googleapis.com/golang/go1.4.3.linux-amd64.tar.gz | tar -C /go1.4-amd64 -zxv \
+	) \
+	&& mv /go1.4-amd64/go /go1.4 \
+	&& rm -rf /go1.4-amd64 \
+	&& rm -rf /go1.4/pkg/linux_amd64_race \
+		/go1.4/api \
+		/go1.4/blog \
+		/go1.4/doc \
+		/go1.4/misc \
+		/go1.4/test \
+	&& find /go1.4 -type d -name testdata | xargs rm -rf
+
+RUN curl -o /usr/local/bin/stage0 https://storage.googleapis.com/go-builder-data/buildlet-stage0.linux-amd64-kube \
+	&& chmod +x /usr/local/bin/stage0
+
+ENV GOROOT_BOOTSTRAP=/go1.4 GOOS=linux GOARCH=arm CC_FOR_TARGET=arm-linux-gnueabihf-gcc

env/crosscompile/linux-armhf-stretch/Makefile

@@ -0,0 +1,25 @@
+# Copyright 2016 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.
+
+IMAGE_NAME=$(shell basename $(CURDIR))
+STAGING_REPO=gcr.io/go-dashboard-dev
+PROD_REPO=gcr.io/symbolic-datum-552
+
+usage:
+	echo "Use staging, prod, or dev targets. For dev, specify your Docker repository with the REPO=foo argument." ; exit 1
+
+staging: Dockerfile
+	docker build -t $(STAGING_REPO)/$(IMAGE_NAME):latest .
+	gcloud docker push $(STAGING_REPO)/$(IMAGE_NAME):latest
+
+prod: Dockerfile
+	docker build -t $(PROD_REPO)/$(IMAGE_NAME):latest .
+	gcloud docker push $(PROD_REPO)/$(IMAGE_NAME):latest
+
+# You must provide a REPO=your-repo-name arg when you make
+# this targarget. REPO is the name of the Docker repository
+# that will be prefixed to the name of the image being built.
+dev: Dockerfile
+	docker build -t $(REPO)/$(IMAGE_NAME):latest .
+	gcloud docker push $(REPO)/$(IMAGE_NAME):latest

env/crosscompile/linux-armhf-stretch/README

@@ -0,0 +1,2 @@
+The docker image created from this directory can be used to cross compile go
+from linux/amd64 to linux/armhf.