jemalloc: Add 'lib' to cmake path suffixes

Change-Id: Ida983e86def551d953f8f1afe720aff55f327f87
Reviewed-on: http://review.couchbase.org/39997
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>