Build a 32-bit version of yabridge on the CI

Specially for @AVLinux. We currently don't build a 32-bit version of
yabridgectl though, so you'd still need that if you want to use yabridge
on an _actual_ 32-bit system.

.github/workflows/build.yml

@@ -99,6 +99,44 @@ jobs:
           name: ${{ env.ARCHIVE_NAME }}
           path: ${{ env.ARCHIVE_NAME }}
 
+  # The same as `build-bionic`, but for a 32-bit only version of yabridge. We
+  # don't plan on distributing this, but we'll just have this available for AV
+  # Linux. We currently don't do 32-bit builds of yabridgectl though.
+  build-32-bit:
+    name: Build on Ubuntu 18.04 (32-bit build)
+    runs-on: ubuntu-latest
+    container: robbert/docker-yabridge:bionic
+    outputs:
+      artifact-name: ${{ env.ARCHIVE_NAME }}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Fetch all git history
+        run: git fetch --force --prune --tags --unshallow
+      - name: Determine build archive name
+        run: |
+          echo "ARCHIVE_NAME=yabridge-$(git describe --always)-ubuntu-18.04-32bit.tar.gz" >> "$GITHUB_ENV"
+      - name: Build the binaries
+        run: |
+          mkdir -p /tmp/prefix
+          export WINEPREFIX=/tmp/prefix
+
+          # Statically link to libstdc++ on Ubuntu 18.04, and also target a
+          # 32-bit OS
+          meson setup build --buildtype=release --cross-file=cross-wine.conf --unity=on --unity-size=10000 -Dwith-static-boost=true -Dwith-bitbridge=true -Dcpp_link_args='-mwindows -static-libstdc++' -Dbuild.cpp_args='-m32' -Dbuild.cpp_link_args='-m32 -static-libstdc++'
+          ninja -C build
+      - name: Create an archive for the binaries
+        run: |
+          mkdir yabridge
+          cp build/libyabridge-{vst2,vst3}.so build/yabridge-{host,group}{,-32}.exe{,.so} yabridge
+          cp CHANGELOG.md README.md yabridge
+
+          tar -caf "$ARCHIVE_NAME" yabridge
+          rm -rf yabridge
+      - uses: actions/upload-artifact@v2
+        with:
+          name: ${{ env.ARCHIVE_NAME }}
+          path: ${{ env.ARCHIVE_NAME }}
+
   build-yabridgectl:
     name: Build yabridgectl
     runs-on: ubuntu-18.04