.github/workflows: add tsconnect static build to wasm GitHub action

Technically not the same as the wasm cross-compilation, but it's
closely connected to it.

Also includes some fixes to tool/yasm to make it actually work on
non-ARM platforms.

Fixes #5134

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

.github/workflows/cross-wasm.yml

@@ -31,6 +31,11 @@ jobs:
         GOARCH: wasm
       run: go build ./cmd/tsconnect/wasm
 
+    - name: tsconnect static build
+      # Use our custom Go toolchain, we set build tags (to control binary size)
+      # that depend on it.
+      run: ./tool/go run ./cmd/tsconnect build
+
     - uses: k0kubun/action-slack@v2.0.0
       with:
         payload: |