message: Abort via report_fatal_error if dialect has been registered.
  Fixes test in opt mode.
  Closes:
diff: @@ -703,11 +703,14 @@ void Dialect::registerDialect(MLIRContext *context) {
  // Lock access to the context registry.
  llvm::sys::SmartScopedWriter<true> registryLock(impl.contextMutex);
  - assert(llvm::none_of(impl.dialects,
  - [this](std::unique_ptr<Dialect> &dialect) {
  + // Abort if dialect with namespace has already been registered.
  + if (llvm::any_of(impl.dialects, [this](std::unique_ptr<Dialect> &dialect) {
  return dialect->getNamespace() == getNamespace();
  - }) &&
  - "a dialect with the given namespace has already been registered");
  + })) {
  + llvm::report_fatal_error("a dialect with namespace '" +
  + Twine(getNamespace()) +
  + "' has already been registered");
  + }
  impl.dialects.push_back(std::unique_ptr<Dialect>(this));
  }
  