Github Actions: switch to using Docker

Many of the free-to-use CI systems work great, but lack environments
which are up to date.  Github Actions is no exception, alas.

In order to ensure that newer version of libraries can be accessed, use
a Docker environment.  The one Github Actions uses is stored on
fvwmorg's Package site, which has pre-existing libraries installed.

Any updates to dependencies will mean that the fvwm3-build:latest docker
environment will need updating.

.github/workflows/ccpp.yml

@@ -9,11 +9,15 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-    - name: install
-      run: |
-        sudo apt install autotools-dev build-essential debhelper dh-autoreconf file fontconfig gettext libfontconfig-dev libfreetype6-dev libfribidi-dev libncurses5-dev libpng-dev libreadline-dev libsm-dev libx11-dev libxcursor-dev libxext-dev libxft-dev libxi-dev libxpm-dev libxrandr-dev libxrender-dev libxt-dev sharutils xsltproc
-        (./autogen.sh && CFLAGS= ./configure)
-        make CFLAGS="-g -O2 -Wall"
+      with:
+        repo-token: ${{ secrets.FVWM3_READ_TOKEN }}
+    - name: Docker Login
+      run: docker login docker.pkg.github.com -u $GITHUB_ACTOR -p ${{ secrets.FVWM3_READ_TOKEN }}
+    - name: Pulling docker image
+      run: docker pull docker.pkg.github.com/smoothwall/build-core/build-base:latest
+    - name: Build Package
+      run: 'docker build -t fvwm3 .'
+
   notification:
     runs-on: ubuntu-latest
     name: notifications

Dockerfile

@@ -0,0 +1,6 @@
+FROM docker.pkg.github.com/fvwmorg/fvwm3/fvwm3-build:latest
+
+COPY . /build
+WORKDIR /build
+
+RUN ./autogen.sh && ./configure && make