Build dotnet with GitHub Actions

Signed-off-by: Ilya Leoshkevich <[email protected]>

.github/workflows/dotnet.yml

@@ -0,0 +1,29 @@
+name: Build dotnet
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:  # XXX
+
+jobs:
+  toolchain:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        arch: [ppc64le, s390x, x64]
+    container:
+      image: ghcr.io/ibm/dotnet-${{ matrix.arch }}-toolchain:latest
+      credentials:
+         username: ${{ secrets.GHCR_USERNAME }}
+         password: ${{ secrets.GHCR_PASSWORD }}
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1  # newer versions are not compatible with Ubuntu 18.04
+    - name: Configure git
+      run: git config user.email [email protected] &&
+           git config user.name "dotnet-s390x bot"
+    - name: Prepare
+      run: ./dotnet-prepare
+    - name: Build
+      run: ARCH=${{ matrix.arch }} NO_SAVE_TEMPS=1 ./dotnet-build