Create Linux dev release job

Job uses Ubuntu 16.04 to get the widest compatibiity with Linux
distributions.

Snapshot builds are uploaded as job artifacts, but GitHub Actions do not
allow to specify compression program/params yet (everything is forced
into a zip).

.github/workflows/linux.yml

@@ -38,3 +38,41 @@ jobs:
         env:
           MAX_WARNINGS: ${{ matrix.conf.max_warnings }}
         run:  ./scripts/count-warnings.py build.log
+
+  build_linux_release_dynamic:
+    name: Release build (dynamic)
+    runs-on: ubuntu-16.04
+    steps:
+      - uses: actions/checkout@v1
+      - run:  sudo apt-get update
+      - name: Install C++ compiler and libraries
+        run:  sudo apt-get install -y tree $(./scripts/list-build-dependencies.sh -m apt -c gcc)
+      - name: Log environment
+        run:  ./scripts/log-env.sh
+      - name: Build
+        run: |
+          set -x
+          export VERSION=$(git describe --abbrev=4)
+          sed -i "s/AC_INIT(dosbox,git)/AC_INIT(dosbox,$VERSION)/" configure.ac
+          ./autogen.sh
+          ./configure CXXFLAGS="-O3 -DNDEBUG"
+          make -j "$(nproc)"
+          strip src/dosbox
+          install -DT        src/dosbox    dest/dosbox
+          install -DT -m 644 COPYING       dest/COPYING
+          install -DT -m 644 README        dest/doc/manual.txt
+          install -DT -m 644 docs/dosbox.1 dest/man/dosbox.1
+          mv dest "dosbox-staging-$VERSION"
+          tree --si -p "dosbox-staging-$VERSION"
+          tar -cJf "dosbox-staging-$VERSION.tar.xz" "dosbox-staging-$VERSION"
+          # Inject variable into the surrounding env in workflow,
+          # otherwise it won't be usable in the next step.
+          echo ::set-env name=VERSION::$VERSION
+      - name: Upload tarball artifact
+        uses: actions/upload-artifact@master
+        # GitHub automatically zips the artifacts (there's no way to create
+        # a tarball), and it removes all executable flags while zipping.
+        # Letting it zip a tarball preserves flags in the compressed files.
+        with:
+          name: ${{ env.VERSION }}-linux-x86_64
+          path: dosbox-staging-${{ env.VERSION }}.tar.xz