Fix build breakage on windows

Context: pthreads

Change-Id: If9d6bc020b525e90334d0c374699ee43e1324626
Reviewed-on: http://review.couchbase.org/44138
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>