Don't add -pedantic for g++ < 4.5

Change-Id: I699e5aa39ee9c05297d8474a05dfa4251d7309d6
Reviewed-on: http://review.couchbase.org/34884
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>