Add CMake SDL builds to CI workflow.

.github/workflows/build.yml

@@ -1,8 +1,8 @@
 name: Build
 on: [pull_request]
 jobs:
-  build-mac:
-    name: Mac UI on ${{ matrix.os }}
+  build-mac-xcodebuild:
+    name: Mac UI / xcodebuild / ${{ matrix.os }}
     strategy:
       matrix:
         os: [macos-latest]
@@ -13,8 +13,44 @@ jobs:
     - name: Make
       working-directory: OSBindings/Mac
       run: xcodebuild CODE_SIGN_IDENTITY=-
-  build-sdl:
-    name: SDL UI on ${{ matrix.os }}
+  build-sdl-cmake:
+    name: SDL UI / cmake / ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Install dependencies
+      shell: bash
+      run: |
+        case $RUNNER_OS in
+          Linux)
+            sudo apt-get --allow-releaseinfo-change update
+            sudo apt-get --fix-missing install cmake gcc-10 libsdl2-dev
+            ;;
+          macOS)
+            brew install cmake sdl2
+            ;;
+        esac
+    - name: Make
+      shell: bash
+      run: |
+        case $RUNNER_OS in
+          Linux)
+            jobs=$(nproc --all)
+            ;;
+          macOS)
+            jobs=$(sysctl -n hw.activecpu)
+            ;;
+          *)
+            jobs=1
+        esac
+        cmake -S. -Bbuild -DCLK_UI=SDL -DCMAKE_BUILD_TYPE=Release
+        cmake --build build -v -j"$jobs"
+  build-sdl-scons:
+    name: SDL UI / scons / ${{ matrix.os }}
     strategy:
       matrix:
         os: [macos-latest, ubuntu-latest]