message: log: Don't use the logger before building it.
diff: @@ -200,8 +200,8 @@ namespace elle
  auto const level = os::getenv("ELLE_LOG_LEVEL", "LOG"s);
  _logger() = std::make_unique<TextLogger>(std::cerr, level);
  auto const ts = os::getenv("ELLE_LOG_TARGETS", "stderr://?" + level);
  - ELLE_DUMP("building main logger: {}", ts)
  _logger() = make_logger(ts);
  + ELLE_DUMP("built main logger: {}", ts);
  }
  return *_logger();
  }
  