osx: snapview-server fails to build on OSX use 'syscall.h'

Change-Id: I29aeb32a972ed6d19e779b9e79fce9a489848497
BUG: 1089172
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/8436
Tested-by: Gluster Build System <jenkins@build.gluster.com>