ci: add workflow to build spirv_to_dxil.dll from Mesa

Reproducible Windows x64 build of Mesa's spirv_to_dxil library.
Workflow produces an artifact that can be downloaded and checked in
to sources/shaders/Stride.Shaders.Compilers/native/.

Minimal Meson config (no LLVM, no Vulkan drivers, no Gallium) —
only builds the spirv_to_dxil target.

Author: xen2

.github/workflows/dep-spirv-to-dxil.yml

@@ -0,0 +1,85 @@
+name: "Dep: Build spirv_to_dxil (Mesa)"
+
+on:
+  workflow_dispatch:
+    inputs:
+      repository:
+        description: Mesa repository to build (fork or upstream)
+        default: stride3d/mesa
+        required: false
+      branch:
+        description: Mesa branch/ref to build
+        default: main
+        required: false
+
+jobs:
+  build-windows:
+    name: Build spirv_to_dxil (Windows x64)
+    runs-on: windows-2025-vs2026
+    steps:
+      - name: Checkout Mesa
+        uses: actions/checkout@v4
+        with:
+          repository: ${{ github.event.inputs.repository || 'stride3d/mesa' }}
+          ref: ${{ github.event.inputs.branch || 'main' }}
+          path: mesa-src
+
+      - name: Install build dependencies
+        shell: pwsh
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install meson ninja mako
+
+      - name: Setup MSVC environment
+        uses: ilammy/msvc-dev-cmd@v1
+        with:
+          arch: x64
+
+      - name: Configure Mesa
+        shell: cmd
+        working-directory: mesa-src
+        run: |
+          set PYTHONUTF8=1
+          meson setup _build ^
+            --default-library=shared ^
+            --buildtype=release ^
+            --wrap-mode=default ^
+            -Dshared-glapi=disabled ^
+            -Dgles1=disabled ^
+            -Dgles2=disabled ^
+            -Dopengl=false ^
+            -Degl=disabled ^
+            -Dglx=disabled ^
+            -Dvulkan-drivers= ^
+            -Dgallium-drivers= ^
+            -Dplatforms= ^
+            -Dmicrosoft-clc=disabled ^
+            -Dspirv-to-dxil=true ^
+            -Dbuild-tests=false ^
+            -Dllvm=disabled
+
+      - name: Build
+        shell: cmd
+        working-directory: mesa-src
+        run: |
+          set PYTHONUTF8=1
+          meson compile -C _build spirv_to_dxil
+
+      - name: Collect DLL
+        shell: pwsh
+        run: |
+          New-Item -ItemType Directory -Force -Path out | Out-Null
+          $dll = Get-ChildItem -Recurse mesa-src/_build -Filter spirv_to_dxil.dll | Select-Object -First 1
+          Copy-Item $dll.FullName out/spirv_to_dxil.dll
+          $pdb = Get-ChildItem -Recurse mesa-src/_build -Filter spirv_to_dxil.pdb -ErrorAction SilentlyContinue | Select-Object -First 1
+          if ($pdb) { Copy-Item $pdb.FullName out/spirv_to_dxil.pdb }
+          # Record commit for traceability
+          $commitHash = git -C mesa-src rev-parse HEAD
+          "Mesa commit: $commitHash" | Out-File out/VERSION.txt
+          Get-ChildItem out
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: spirv_to_dxil-win-x64
+          path: out/