CBD-926: Always build with iSASL support

Change-Id: I061b34c9edb4a7d21b25c54236f9847b16e226d5
Reviewed-on: http://review.couchbase.org/25358
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>