Codechange: [CI] Split the ci-build into smaller components

.github/workflows/ci-emscripten.yml

@@ -0,0 +1,62 @@
+name: CI (Emscripten)
+
+on:
+  workflow_call:
+
+env:
+  CTEST_OUTPUT_ON_FAILURE: 1
+
+jobs:
+  emscripten:
+    name: CI
+
+    runs-on: ubuntu-20.04
+    container:
+      # If you change this version, change the number in the cache step too.
+      image: emscripten/emsdk:3.1.42
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+
+    - name: Setup cache
+      uses: actions/cache@v4
+      with:
+        path: /emsdk/upstream/emscripten/cache
+        key: 3.1.42-${{ runner.os }}
+
+    - name: Patch Emscripten to support LZMA
+      run: |
+        cd /emsdk/upstream/emscripten
+        patch -p1 < ${GITHUB_WORKSPACE}/os/emscripten/emsdk-liblzma.patch
+
+    - name: Build (host tools)
+      run: |
+        mkdir build-host
+        cd build-host
+
+        echo "::group::CMake"
+        cmake .. -DOPTION_TOOLS_ONLY=ON
+        echo "::endgroup::"
+
+        echo "::group::Build"
+        echo "Running on $(nproc) cores"
+        cmake --build . -j $(nproc) --target tools
+        echo "::endgroup::"
+
+    - name: Install GCC problem matcher
+      uses: ammaraskar/gcc-problem-matcher@master
+
+    - name: Build
+      run: |
+        mkdir build
+        cd build
+
+        echo "::group::CMake"
+        emcmake cmake .. -DHOST_BINARY_DIR=../build-host
+        echo "::endgroup::"
+
+        echo "::group::Build"
+        echo "Running on $(nproc) cores"
+        cmake --build . -j $(nproc) --target openttd
+        echo "::endgroup::"