ci: add docker spec to build ninja for linux-aarch64

.gitlab/ci/docker/ninja/centos7-aarch64.bash

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+
+set -e
+set -x
+
+cleanup() {
+    docker container rm -fv "$build_container" >/dev/null 2>&1 || true
+    docker image rm -f "$build_image" >/dev/null 2>&1 || true
+}
+
+readonly suffix="-$(date -u +%Y-%m-%d)-${RANDOM}"
+readonly build_container="ninja-build-linux-aarch64$suffix"
+readonly build_image="ninja:build-linux-aarch64$suffix"
+readonly git_tag="${1-v1.10.2}"
+
+trap "cleanup" EXIT INT TERM
+
+docker image build --build-arg GIT_TAG="$git_tag" --tag="$build_image" "${BASH_SOURCE%/*}/centos7-aarch64"
+docker container create --name "$build_container" "$build_image"
+docker cp "$build_container:/ninja/ninja" "ninja"

.gitlab/ci/docker/ninja/centos7-aarch64/Dockerfile

@@ -0,0 +1,7 @@
+FROM kitware/cmake:build-linux-aarch64-base-2020-12-21
+MAINTAINER Brad King <brad.king@kitware.com>
+
+ARG GIT_TAG=v1.10.2
+
+COPY build_ninja.sh /root/build_ninja.sh
+RUN scl enable devtoolset-7 -- sh /root/build_ninja.sh $GIT_TAG

.gitlab/ci/docker/ninja/centos7-aarch64/build_ninja.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+set -e
+
+git clone https://github.com/ninja-build/ninja.git
+cd ninja
+git checkout "${1-v1.10.2}"
+./configure.py --bootstrap
+./ninja all
+./ninja_test
+strip ninja