message: warn on unused exception parameter
  Summary:
  The Windows build spews a great many warnings. Address some of them by
  enabling the unused-exception-parameter warning on Clang/Linux too.
diff: @@ -108,7 +108,7 @@ class BaseService : virtual public cpp2::BaseServiceSvIf {
  int64_t getCounter(std::unique_ptr<std::string> key) override {
  try {
  return ServiceData::get()->getCounter(*key);
  - } catch (const std::invalid_argument& ex) {
  + } catch (const std::invalid_argument&) {
  return 0;
  }
  }
  