Add ubuntu build action

.github/workflows/build-linux.yml

@@ -0,0 +1,32 @@
+name: rottexpr build: Ubuntu 64bit latest
+
+on:
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+  workflow_dispatch:
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+
+    - name: Install dependencies
+      run: |
+          sudo apt-get update
+          sudo apt-get install -y libsdl2-dev libsdl2-mixer-dev
+
+    - name: Build rottexpr
+      working-directory: src
+      run: make
+
+    - name: Upload binary as artifact
+      uses: actions/upload-artifact@v4
+      with:
+        name: rott-ubuntu64-binary
+        path: src/rott