snort: add missing pkgconfig inherit

* otherwise m4 eats all memory and is killed by OOMK
  [1051138.019784] Out of memory: Kill process 26264 (m4) score 860 or sacrifice child
  [1051138.019788] Killed process 26264 (m4) total-vm:23062712kB, anon-rss:15066516kB, file-rss:100kB

* very strange, but m4 and snort sometimes have strange side-effects,
  from first google result:
  http://www.hipforums.com/newforums/showthread.php?t=466568



Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>