GHA: Add workflow for testing bootstrap with every release from D 2.076.1

.github/workflows/bootstrap.yml

@@ -0,0 +1,76 @@
+# https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions
+
+name: Bootstrap
+on:
+  pull_request:
+    branches:
+      - stable
+  push:
+    branches:
+      - master
+      - stable
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  main:
+    strategy:
+      fail-fast: false
+      matrix:
+        version: [
+                                                                2.076.1, 2.077.1, 2.078.3, 2.079.1,
+          2.080.1, 2.081.2, 2.082.1, 2.083.1, 2.084.1, 2.085.1, 2.086.1, 2.087.1, 2.088.1, 2.089.1,
+          2.090.1, 2.091.1, 2.092.1, 2.093.1, 2.094.2, 2.095.1, 2.096.1, 2.097.2, 2.098.1, 2.099.1,
+          2.100.2, 2.101.2, 2.102.2, 2.103.1, 2.104.2, 2.105.3, 2.106.1, 2.107.1
+        ]
+
+    name: Build with dmd-${{ matrix.version }}
+    runs-on: ubuntu-22.04
+    timeout-minutes: 10
+    env:
+      # for ci/run.sh:
+      OS_NAME: linux
+      MODEL: 64
+      HOST_DMD: dmd-${{ matrix.version }}
+      # N is set dynamically below
+      FULL_BUILD: true
+    defaults:
+      run:
+        shell: bash
+
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 50
+
+    - name: Set environment variable N (parallelism)
+      run: echo "N=$(nproc)" >> $GITHUB_ENV
+
+    - name: Install host compiler
+      run: ci/run.sh install_host_compiler
+
+    - name: Set up repos
+      run: |
+        set -uexo pipefail
+        ref='${{ github.ref }}'
+        if [[ "$ref" =~ ^refs/pull/ ]]; then
+          # PR: clone the Phobos head with the same name as this DMD PR's target branch
+          # e.g., Phobos stable when targeting DMD stable
+          REPO_BRANCH="$GITHUB_BASE_REF"
+        elif [[ "$ref" =~ ^refs/(heads|tags)/(.*)$ ]]; then
+          # no PR: try to clone the Phobos head with the same name as this DMD head, falling back to master
+          # e.g., Phobos stable for a push to DMD stable, or Phobos v2.105.2 for DMD tag v2.105.2
+          REPO_BRANCH="${BASH_REMATCH[2]}"
+        else
+          echo "Error: unexpected GitHub ref '$ref'" >&2
+          exit 1
+        fi
+        ci/run.sh setup_repos "$REPO_BRANCH"
+
+    - name: Build dmd
+      run: ENABLE_RELEASE=0 ENABLE_DEBUG=0 ci/run.sh build 0
+
+    - name: Rebuild dmd
+      run: ENABLE_RELEASE=0 ENABLE_DEBUG=0 ci/run.sh rebuild