message: [lldb] Replace std::call_once() with llvm::call_once()
  Remove the single instance of std::call_once() in lldbTarget library
  with llvm::call_once().  The former fails to build on NetBSD when
  combined with llvm::once_flag (which replaced std::once_flag
  in r369618), and combining the two is probably generally incorrect
  anyway.
diff: @@ -5965,7 +5965,7 @@ UtilityFunction *Process::GetLoadImageUtilityFunction(
  llvm::function_ref<std::unique_ptr<UtilityFunction>()> factory) {
  if (platform != GetTarget().GetPlatform().get())
  return nullptr;
  - std::call_once(m_dlopen_utility_func_flag_once,
  + llvm::call_once(m_dlopen_utility_func_flag_once,
  [&] { m_dlopen_utility_func_up = factory(); });
  return m_dlopen_utility_func_up.get();
  }
  