add CI for GP2X also

no helix as it has (had?) weird license IIRC

.github/workflows/ci-gp2x.yml

@@ -0,0 +1,20 @@
+name: CI (GP2X)
+on: [push, pull_request]
+jobs:
+  build-linux:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: true
+    - name: Install dependencies
+      run: |
+        whoami
+        sudo apt-get update -qq
+        sudo apt-get install -y wget
+        wget http://notaz.gp2x.de/downloads/gp2x/devkitGP2X_small.tar.xz
+        tar -C /tmp/ -xf devkitGP2X_small.tar.xz
+    - name: configure
+      run: DUMP_CONFIG_LOG=1 PATH=$PATH:/tmp/devkitGP2X/bin CROSS_COMPILE=arm-linux- ./configure --platform=gp2x
+    - name: make
+      run: PATH=$PATH:/tmp/devkitGP2X/bin CROSS_COMPILE=arm-linux- make PLATFORM_MP3=0