ci: add auto build ci

.gitea/workflows/build.yml

@@ -0,0 +1,28 @@
+name: Build nix packages
+on: [push]
+
+jobs:
+  build-matrix:
+    runs-on: nix
+    strategy:
+      matrix:
+        package: [ "am-kernels", "rv32Cross.am-kernels-nemu", "rv32Cross.am-kernels-npc" ]
+    steps:
+      - uses: https://github.com/cachix/cachix-action@v14
+        with:
+          name: ysyx
+          authToken: '${{ secrets.CACHIX_SIGNING_KEY }}'
+      - uses: actions/checkout@v4
+      - name: Cache develop environment
+        id: cache-nix-develop
+        uses: actions/cache@v4
+        with:
+          path: |
+            /nix/store
+            /nix/var/nix/db
+          key: nix-develop-${{ hashFiles('flake.*') }}
+
+      - name: Build am-kernels
+        run: |
+          nix build .#{am-kernels}
+          nix build .#rv32Cross.{am-kernels-nemu, am-kernels-npc}