Add arm64 to releases

This moves all the release builds into a Dockerfile which is a bit
cleaner for setting up our build environment.

Non-linux/amd64 builds are cross-compiled.
Currently onlinux linux/amd64, linux/arm64, and windows/amd64 are
supported, but is easy to add more, provided their is a cross-compile
toolchain available for it.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

script/setup/install-runhcs-shim

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+
+#   Copyright The containerd Authors.
+
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+
+#       http://www.apache.org/licenses/LICENSE-2.0
+
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+
+: ${RUNHCS_VERSION:="$(grep 'Microsoft/hcsshim ' go.mod | awk '{print $2}')"}
+: ${RUNHCS_REPO:="https://github.com/Microsoft/hcsshim.git"}
+: ${DESTDIR:=''}
+: ${GOOS:="windows"}
+
+tmpdir="$(mktemp -d)"
+
+cleanup() {
+    rm -rf "$tmpdir"
+}
+
+trap 'cleanup' EXIT
+
+export GOOS
+
+(
+    set -e -x
+    cd "$tmpdir"
+    git init .
+    git remote add origin "$RUNHCS_REPO"
+    git fetch --tags --depth=1 origin ${RUNHCS_VERSION}
+    git checkout "refs/tags/${RUNHCS_VERSION}" || git checkout "refs/heads/${RUNHCS_VERSION}" || git checkout "${RUNHCS_VERSION}"
+    GO111MODULE=on go build -mod=vendor -o "${DESTDIR}/containerd-shim-runhcs-v1.exe" ./cmd/containerd-shim-runhcs-v1
+)