github: Install libltdl-dev in the linux-cross-windows build job

This is required for building libffi. With ubuntu-22.04 images,
the libltdl-dev package was available out of the box.

Also explicitly install swig, which we rely on - this also seems
to have been available implicitly.

.github/workflows/build.yml

@@ -314,7 +314,7 @@ jobs:
           SOURCE_DATE_EPOCH: ${{needs.prepare.outputs.COMMIT_DATE_UNIX}}
           BUILD_DATE: ${{needs.prepare.outputs.BUILD_DATE}}
         run: |
-          sudo apt-get update && sudo apt-get install autoconf-archive ninja-build
+          sudo apt-get update && sudo apt-get install libltdl-dev swig autoconf-archive ninja-build
           ./build-cross-tools.sh /opt/llvm-mingw $(pwd)/install/llvm-mingw ${{matrix.arch}} --with-python
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           cd install