Added some cross-os builds

.github/workflows/test.yaml

@@ -34,3 +34,24 @@ jobs:
         run: GOARCH=arm go build -v ./...
         shell: bash
 
+  cross-os-build:
+    strategy:
+      matrix:
+        go-os-pairs:
+          - "freebsd amd64"
+          - "openbsd amd64"
+          - "openbsd 386"
+          - "openbsd arm"
+
+    runs-on: "ubuntu-latest"
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions/setup-go@v1
+        with:
+          go-version: "1.13"
+      - name: Cross-build
+        run: |
+          set ${{ matrix.go-os-pairs }}
+          GOOS=$1 GOARCH=$2 go build -v ./...
+        shell: bash