Feature: [Actions / CMake] support for generic linux builds (#8641)

These bundles can be opened on any "modern" Linux machine with
a driver that SDL2 supports.

Machines needs at least glibc 2.15, which was released 10 years ago.
It is build with CentOS 7 as base, and only assumes the following
libraries are available on the system:
- libc
- libdl
- libgcc_s
- libpthread
- librt
- libstdc++

All other libraries the game depends on are bundled together with
the game, so users don't need any library installed to use this
bundle. The downside of course is that this increases the binary
size a bit: 30 MiB of libraries are in this bundle.

RPATH is used to make ld-linux find the folder libraries are
stored in; however, system libraries are always used before these,
in the assumption libraries on the user system are more up-to-date.

Using -DOPTION_PACKAGE_DEPENDENCIES=ON switches on packaging
of libraries in the "lib" folder. This requires CMake 3.16 to
be installed; otherwise it will fail.

.github/workflows/release.yml

@@ -265,7 +265,93 @@ jobs:
         retention-days: 5
 
   linux:
-    name: Linux
+    name: Linux (Generic)
+    needs: source
+
+    runs-on: ubuntu-20.04
+    container:
+      # manylinux2014 is based on CentOS 7, but already has a lot of things
+      # installed and preconfigured. It makes it easier to build OpenTTD.
+      image: quay.io/pypa/manylinux2014_x86_64
+
+    steps:
+    - name: Download source
+      uses: actions/download-artifact@v2
+      with:
+        name: internal-source
+
+    - name: Unpack source
+      run: |
+        tar -xf source.tar.gz --strip-components=1
+
+    - name: Install dependencies
+      run: |
+        echo "::group::Install dependencies"
+        yum install -y \
+          fontconfig-devel \
+          freetype-devel \
+          libicu-devel \
+          libpng-devel \
+          libpng-devel \
+          lzo-devel \
+          SDL2-devel \
+          wget \
+          xz-devel \
+          zlib-devel \
+          # EOF
+        echo "::endgroup::"
+
+        # The yum variant of fluidsynth depends on all possible audio drivers.
+        # This is not really useful for us, as that would require a user to
+        # have them all before he can start OpenTTD. Instead, compile a
+        # version that can only use SDL2. As OpenTTD does sound via SDL2,
+        # this simply means we either have sound and music, or have none.
+        echo "::group::Install fluidsynth"
+        wget https://github.com/FluidSynth/fluidsynth/archive/v2.1.6.tar.gz
+        tar xf v2.1.6.tar.gz
+        (
+          cd fluidsynth-2.1.6
+          mkdir build
+          cd build
+          cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_INSTALL_PREFIX=/usr
+          make -j$(nproc)
+          make install
+        )
+        echo "::endgroup::"
+
+    - name: Install GCC problem matcher
+      uses: ammaraskar/gcc-problem-matcher@master
+
+    - name: Build
+      run: |
+        mkdir -p build
+        cd build
+
+        echo "::group::CMake"
+        cmake ${GITHUB_WORKSPACE} \
+          -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+          -DOPTION_PACKAGE_DEPENDENCIES=ON \
+          # EOF
+        echo "::endgroup::"
+
+        echo "::group::Build"
+        echo "Running on $(nproc) cores"
+        make -j$(nproc) package
+        echo "::endgroup::"
+
+        # Remove the sha256 files CPack generates; we will do this ourself at
+        # the end of this workflow.
+        rm -f bundles/*.sha256
+
+    - name: Store bundles
+      uses: actions/upload-artifact@v2
+      with:
+        name: openttd-linux-generic
+        path: build/bundles
+        retention-days: 5
+
+  linux-distro:
+    name: Linux (Distros)
     needs: source
 
     if: needs.source.outputs.is_tag == 'true'
@@ -633,6 +719,7 @@ jobs:
     - source
     - docs
     - linux
+    - linux-distro
     - macos
     - windows
 
@@ -641,7 +728,7 @@ jobs:
     # "always()" is important here, it is the keyword to use to stop skipping
     # this job if any dependency is skipped. It looks a bit silly, but it is
     # how GitHub Actions work ;)
-    if: always() && needs.source.result == 'success' && needs.docs.result == 'success' && (needs.linux.result == 'success' || needs.linux.result == 'skipped') && needs.macos.result == 'success' && needs.windows.result == 'success'
+    if: always() && needs.source.result == 'success' && needs.docs.result == 'success' && needs.linux.result == 'success' && (needs.linux-distro.result == 'success' || needs.linux-distro.result == 'skipped') && needs.macos.result == 'success' && needs.windows.result == 'success'
 
     runs-on: ubuntu-20.04