Add cross-compile workflow for out-of-source ARM build testing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hsbt

.github/workflows/crosscompile.yml

@@ -0,0 +1,105 @@
+name: Cross compile
+on:
+  push:
+    paths-ignore:
+      - 'doc/**'
+      - '**/man/*'
+      - '**.md'
+      - '**.rdoc'
+      - '**/.document'
+      - '.*.yml'
+  pull_request:
+    # Do not use paths-ignore for required status checks
+    # https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/collaborating-on-repositories-with-code-quality-features/troubleshooting-required-status-checks
+  merge_group:
+
+concurrency:
+  group: ${{ github.workflow }} / ${{ startsWith(github.event_name, 'pull') && github.ref_name || github.sha }}
+  cancel-in-progress: ${{ startsWith(github.event_name, 'pull') }}
+
+permissions:
+  contents: read
+
+jobs:
+  make:
+    strategy:
+      matrix:
+        include:
+          - host: aarch64-linux-gnu
+            arch: arm64
+      fail-fast: false
+
+    env:
+      GITPULLOPTIONS: --no-tags origin ${{ github.ref }}
+
+    runs-on: ubuntu-22.04
+
+    if: >-
+      ${{!(false
+      || contains(github.event.head_commit.message, '[DOC]')
+      || contains(github.event.pull_request.title, '[DOC]')
+      || contains(github.event.pull_request.labels.*.name, 'Documentation')
+      || (github.event.pull_request.user.login == 'dependabot[bot]')
+      )}}
+
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          sparse-checkout-cone-mode: false
+          sparse-checkout: /.github
+          persist-credentials: false
+
+      - uses: ./.github/actions/setup/directories
+        with:
+          srcdir: src
+          builddir: build
+          makeup: true
+
+      - name: Install cross-compilation toolchain
+        run: |
+          sudo dpkg --add-architecture ${{ matrix.arch }}
+          sudo apt-get update -qq || :
+          sudo apt-get install --no-install-recommends -qq -y \
+            crossbuild-essential-${{ matrix.arch }} \
+            libssl-dev:${{ matrix.arch }} \
+            libyaml-dev:${{ matrix.arch }} \
+            zlib1g-dev:${{ matrix.arch }} \
+            libffi-dev:${{ matrix.arch }} \
+            libreadline-dev:${{ matrix.arch }} \
+            libncurses-dev:${{ matrix.arch }} \
+            autoconf ruby
+
+      - name: Build baseruby
+        run: |
+          mkdir ../baseruby
+          cd ../baseruby
+          ../src/configure --prefix=$PWD/install --disable-install-doc
+          make
+          make install
+
+      - name: Run configure
+        run: >-
+          ../src/configure -C --disable-install-doc
+          --prefix=/usr
+          --build=x86_64-linux-gnu
+          --host=${{ matrix.host }}
+          --with-baseruby=$PWD/../baseruby/install/bin/ruby
+
+      - run: make
+
+      - run: make install DESTDIR=$PWD/install
+
+      - name: Verify cross-compiled binary
+        run: |
+          file install/usr/bin/ruby
+          file install/usr/bin/ruby | grep -q '${{ matrix.host }}\|aarch64'
+
+      - uses: ./.github/actions/slack
+        with:
+          label: cross ${{ matrix.host }}
+          SLACK_WEBHOOK_URL: ${{ secrets.SIMPLER_ALERTS_URL }} # ruby-lang slack: ruby/simpler-alerts-bot
+        if: ${{ failure() }}
+
+defaults:
+  run:
+    working-directory: build