Fix signaler on Windows

cmd/signaller_nounix.go

@@ -0,0 +1,14 @@
+//go:build windows || plan9
+
+package cmd
+
+import (
+	"context"
+)
+
+// Windows and Plan9 don't support SIGUSR1, so we don't need to start a signaler
+func startSignaler(ctx context.Context) func() error {
+	return func() error {
+		return nil
+	}
+}