meta: move cross-compiled builds to their own parallel jobs

And add FreeBSD.

Fixes #37

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

.github/workflows/linux.yml

@@ -28,21 +28,6 @@ jobs:
     - name: Basic build
       run: go build ./cmd/...
 
-    - name: macOS build
-      env:
-        GOOS: darwin
-        GOARCH: amd64
-      run: go build ./cmd/...
-
-    - name: Windows build
-      env:
-        GOOS: windows
-        GOARCH: amd64
-      run: go build ./cmd/...
-
-    - name: Cross-compile tests for other geese
-      run: ./test.sh
-
     - name: Run tests on linux
       run: go test ./...