CI: ubuntu multiarch & musl

.github/workflows/build.yml

@@ -58,6 +58,25 @@ jobs:
       - name: checkout
         uses: actions/checkout@v4
 
+      - name: set up Ubuntu multiarch
+        if: startsWith(matrix.os, 'ubuntu') && matrix.target-apt-arch != 'amd64'
+        run: |
+          readonly DISTRO_CODENAME=$(lsb_release -c | sed -E 's/Codename:\s*//')
+          sudo dpkg --add-architecture "${{ matrix.target-apt-arch }}"
+          sudo sed -i "s/^deb http/deb [arch=$(dpkg-architecture -q DEB_HOST_ARCH)] http/" /etc/apt/sources.list
+          sudo sed -i "s/^deb mirror/deb [arch=$(dpkg-architecture -q DEB_HOST_ARCH)] mirror/" /etc/apt/sources.list
+          for suite in '' '-updates' '-backports' '-security'; do
+            echo "deb [arch=${{ matrix.target-apt-arch }}] http://ports.ubuntu.com/ $DISTRO_CODENAME$suite main universe multiverse" | \
+            sudo tee -a /etc/apt/sources.list >/dev/null
+          done
+
+      - name: cache musl development files
+        if: endsWith(matrix.target, '-musl')
+        uses: awalsh128/cache-apt-pkgs-action@latest
+        with:
+          packages: musl-tools musl-dev:${{ matrix.target-apt-arch }}
+          version: 1.0
+
       - name: cache apt packages
         if: startsWith(matrix.os, 'ubuntu')
         uses: awalsh128/cache-apt-pkgs-action@latest