Build/CI: set up GithubActions build config

.github/workflows/gcc-build.yml

@@ -0,0 +1,34 @@
+name: GCC
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    steps:
+    - uses: actions/checkout@v2
+    - name: Dependencies
+      run: |
+        sudo apt-get update && sudo apt-get install -yq libboost-all-dev g++-10
+        sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 100 --slave /usr/bin/g++ g++ /usr/bin/g++-10
+    - name: Setup
+      run: |
+        mkdir bin
+        cd bin
+        cmake ../ -DWITH_WARNINGS=1 -DWITH_COREDEBUG=0 -DUSE_COREPCH=1 -DUSE_SCRIPTPCH=1 -DTOOLS=1 -DSCRIPTS=static -DSERVERS=1 -DNOJEM=0 -DCMAKE_BUILD_TYPE=Debug -DCMAKE_C_FLAGS="-Werror" -DCMAKE_CXX_FLAGS="-Werror" -DCMAKE_C_FLAGS_DEBUG="-DNDEBUG" -DCMAKE_CXX_FLAGS_DEBUG="-DNDEBUG" -DCMAKE_INSTALL_PREFIX=check_install -DBUILD_TESTING=1
+        cd ..
+    - name: Build
+      run: |
+        cd bin
+        make -j 4 -k && make install
+    - name: Unit tests
+      run: |
+        cd bin
+        make test
+    - name: Check executables
+      run: |
+        cd bin/check_install/bin
+        ./bnetserver --version
+        ./worldserver --version