num_cpu_cores: Prefer getconf over cpuinfo grep, simplify grep usage

    num="$(sysctl -n hw.ncpu 2>/dev/null || true)"

    ;;

  * )

    num="$(grep ^processor /proc/cpuinfo 2>/dev/null | wc -l | xargs)"

    num="$({ getconf _NPROCESSORS_ONLN ||

             grep -c ^processor /proc/cpuinfo; } 2>/dev/null)"

    num="${num#0}"

    ;;

  esac