Windows support (wip): target layer, Microsoft x64 ABI, portable runtime, CI

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -0,0 +1,79 @@
+name: CI
+
+on:
+  push:
+    branches: [main, "ci/**"]
+    tags: ["v*"]
+  pull_request:
+
+env:
+  LLVM_VERSION: 21.1.8
+
+jobs:
+  linux:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install LLVM 21, libclang, tools
+        run: |
+          wget -q https://apt.llvm.org/llvm.sh
+          sudo bash llvm.sh 21
+          sudo apt-get install -y llvm-21-dev libclang-21-dev ninja-build valgrind
+          echo "/usr/lib/llvm-21/bin" >> $GITHUB_PATH
+      - name: Build
+        run: |
+          cmake -S . -B build -G Ninja -DLLVM_DIR=/usr/lib/llvm-21/lib/cmake/llvm -DCMAKE_BUILD_TYPE=Release
+          ninja -C build
+          build/finch version
+      - name: Tests
+        run: tests/run.sh
+      - name: Tests under valgrind
+        run: MEMCHECK=1 tests/run.sh
+      - name: Self-hosting
+        run: tests/boot.sh
+
+  windows:
+    runs-on: windows-2022
+    defaults:
+      run:
+        shell: bash
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ilammy/msvc-dev-cmd@v1
+      - name: Cache LLVM
+        id: cache-llvm
+        uses: actions/cache@v4
+        with:
+          path: C:/llvm
+          key: llvm-${{ env.LLVM_VERSION }}-x86_64-pc-windows-msvc
+      - name: Download LLVM ${{ env.LLVM_VERSION }}
+        if: steps.cache-llvm.outputs.cache-hit != 'true'
+        run: |
+          curl -sSL -o llvm.tar.xz "https://github.com/llvm/llvm-project/releases/download/llvmorg-$LLVM_VERSION/clang+llvm-$LLVM_VERSION-x86_64-pc-windows-msvc.tar.xz"
+          mkdir -p /c/llvm
+          tar -xf llvm.tar.xz -C /c/llvm --strip-components=1
+          rm llvm.tar.xz
+      - name: Build finch.exe
+        run: |
+          echo "C:/llvm/bin" >> $GITHUB_PATH
+          export PATH="/c/llvm/bin:$PATH"
+          cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release -DLLVM_DIR=C:/llvm/lib/cmake/llvm \
+                -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DCMAKE_C_COMPILER=cl -DCMAKE_CXX_COMPILER=cl
+          ninja -C build
+          cp /c/llvm/bin/libclang.dll build/
+          build/finch.exe version
+      - name: Tests
+        run: |
+          export PATH="/c/llvm/bin:$PATH"
+          tests/run.sh
+      - name: Package
+        run: |
+          mkdir -p dist/finch
+          cp build/finch.exe build/libclang.dll dist/finch/
+          cp README.md LICENSE dist/finch/
+          cp -r examples dist/finch/
+          cd dist && 7z a -tzip finch-windows-x64.zip finch > /dev/null
+      - uses: actions/upload-artifact@v4
+        with:
+          name: finch-windows-x64
+          path: dist/finch-windows-x64.zip