libudev: enumerate - sort with qsort()

libudev: enumerate - sort with qsort()

On machines with many thousands of devices:
  $ time find /sys -name uevent | wc -l
  74876

  real      0m33.171s
  user      0m3.329s
  sys       0m29.719s

the current udevtrigger spends minutes sorting the device list:
  $ time /sbin/udevadm trigger --dry-run

  real      4m56.739s
  user      4m45.743s
  sys       0m7.862s

with qsort() it looks better:
  $ time udev/udevadm trigger --dry-run

  real      0m6.495s
  user      0m0.473s
  sys       0m5.923s