Enable MTT over parallel flag (#4998)

.ci/compile.sh

@@ -160,7 +160,13 @@ cmake .. "${flags[@]}"
 echo "::endgroup::"
 
 echo "::group::Build project"
+if [[ $RUNNER_OS == Windows ]]; then
+  # Enable MTT, see https://devblogs.microsoft.com/cppblog/improved-parallelism-in-msbuild/
+  # and https://devblogs.microsoft.com/cppblog/cpp-build-throughput-investigation-and-tune-up/#multitooltask-mtt
+  cmake --build . "${buildflags[@]}" -- -p:UseMultiToolTask=true
+else
   cmake --build . "${buildflags[@]}"
+fi
 echo "::endgroup::"
 
 if [[ $USE_CCACHE ]]; then

.github/workflows/desktop-build.yml

@@ -358,7 +358,9 @@ jobs:
           CMAKE_GENERATOR: '${{env.CMAKE_GENERATOR}}'
           CMAKE_GENERATOR_PLATFORM: 'x64'
           QTDIR: '${{github.workspace}}\Qt\${{matrix.qt_version}}\win64_${{matrix.qt_arch}}'
-        run: .ci/compile.sh --server --release --test --package --parallel 4
+        # No need for --parallel flag, MTT is added in the compile script to let cmake/msbuild manage core count,
+        # project and process parallelism: https://devblogs.microsoft.com/cppblog/improved-parallelism-in-msbuild/
+        run: .ci/compile.sh --server --release --test --package
 
       - name: Upload artifact
         uses: actions/upload-artifact@v4