MB-6463: ask for 64-bit-wide off_t
MB-6463: ask for 64-bit-wide off_t

So that things don't break massively as couchstore is using 64-bit
wide off_t and if we don't ask for 64-bit off_t we'll have 32-bit wide
and off_t corruption will lead to inability to write to couchstore.

Change-Id: Ie421da545536b7b8afbaa97d542a056ce5d7d1cc
Reviewed-on: http://review.couchbase.org/20268
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>

hisundar/ep-engine,daverigby/kv_engine,sriganes/ep-engine,sriganes/ep-engine,jimwwalker/ep-engine,jimwwalker/ep-engine,abhinavdangeti/ep-engine,teligent-ru/ep-engine,abhinavdangeti/ep-engine,owendCB/ep-engine,hisundar/ep-engine,hisundar/ep-engine,jimwwalker/ep-engine,daverigby/kv_engine,daverigby/ep-engine,abhinavdangeti/ep-engine,owendCB/ep-engine,teligent-ru/ep-engine,teligent-ru/ep-engine,jimwwalker/ep-engine,membase/ep-engine,sriganes/ep-engine,couchbase/ep-engine,membase/ep-engine,owendCB/ep-engine,teligent-ru/ep-engine,sriganes/ep-engine,couchbase/ep-engine,daverigby/kv_engine,daverigby/ep-engine,couchbase/ep-engine,couchbase/ep-engine,daverigby/kv_engine,abhinavdangeti/ep-engine,membase/ep-engine,daverigby/ep-engine,abhinavdangeti/ep-engine,hisundar/ep-engine,membase/ep-engine,owendCB/ep-engine,daverigby/ep-engine