Fix build

Dependencies

• [2] NWFDDRUG hydra-queue-runner: Limit concurrent database connections
• [3] X6FOUYFJ int2String -> std::to_string
• [4] O3NM62IZ Support multiple machines files
• [5] 73YR46NJ hydra-queue-runner: Write directly to a binary cache
• [6] BG6PEOB2 Make the output size limit configurable
• [7] NSBNNM77 Add hydra.conf option "nar_buffer_size" to configure memoryTokens limit
• [*] 24BMQDZA Start of single-process hydra-queue-runner

Change contents

• replacement in src/hydra-queue-runner/hydra-queue-runner.cc at line 74
  [3.1380]→[3.1380:1421](∅→∅)
  − : config(std::make_unique<Config>())
  [3.1380]

  [2.0]
  + : config(std::make_unique<::Config>())
• replacement in src/hydra-queue-runner/hydra-queue-runner.cc at line 192
  [3.1775]→[3.1775:1877](∅→∅)
  − (settings.thisSystem == "x86_64-linux" ? "x86_64-linux,i686-linux" : settings.thisSystem)
  [3.1775]

  [3.0]
  + (settings.thisSystem == "x86_64-linux" ? "x86_64-linux,i686-linux" : settings.thisSystem.get())